What Teams Will Have the Best Defensive Lines in 2008?

Exhaustive statistical research has indicated that the defensive line is the most important part of a defense, and it has the most predictive value in forecasting a team's defensive performance. With that in mind, I now look ahead to 2008 and forecast which teams will have the best defensive lines.

In order to make these forecasts, I took each team's Defensive Line Index (DLI) from 2007 and made adjustments based on personnel changes. (refer to the previous post for a more detailed description of DLI)

a. Points were added if a team was upgrading with a player who performed well in the criteria used for DLI.

b. Points were subtracted when a team lost a player high in DLI stats and replaced him with someone worse.

c. Points were added if a defensive line's average age moved closer to the 26-30 age range, which a random sampling demonstrated are the best years of a defensive lineman's career. In other words, teams got points for maturing. Teams that got a lot younger suffered.

d. Points were added on a sliding scale if a team drafted a defensive lineman in the first three rounds, with more points being awarded to higher draft picks.

Thus, The projected 2008 rankings of NFL defensive lines:


1. Minnesota Vikings- 42.6
2. Philadelphia Eagles- 40.7
3. San Diego Chargers- 39.9
4. Seattle Seahawks- 38.9
5. Tampa Bay Buccaneers- 37.9
6. New York Giants- 37.5
7. Dallas Cowboys- 37.0
8. Jacksonville Jaguars- 35.4
9. Green Bay Packers- 34.2
10. Arizona Cardinals- 33.7
11. Baltimore Ravens- 32.4
12. New England Patriots- 31.2
13. Miami Dolphins- 30.8
14. Detroit Lions- 30.1
15. San Francisco 49ers- 29.8
16. Chicago Bears- 28.3
17. Tennessee Titans- 27.1
18. New Orleans Saints- 26.8
19. Indianapolis Colts- 26.8
20. St. Louis Rams- 26.4
21. Washington Redskins- 25.9
22. New York Jets- 25.8
23. Buffalo Bills- 25.6
24. Houston Texans- 25.3
25. Denver Broncos- 25.2
26. Kansas City Chiefs- 24.8
27. Cleveland Browns- 23.1
28. Pittsburgh Steelers- 21.9
29. Carolina Panthers- 19.8
30. Atlanta Falcons- 18.4
31. Cincinnati Bengals- 16.8
32. Oakland Raiders- 15.4


**Now, keep in mind, that DLI is still a new metric, and I'm working on perfecting it. Furthermore, I'm also working on developing better predictive metrics to forecast future performance. Does that sound like hedging? Okay, I'm a little bit guilty. But hey, that's better than those prediction gurus that promise the moon. The bottom line, though, is that a number of reliable statistical measures went into this formula, and I feel good that, barring injuries, the numbers will shape up something like this.**

P.S. As for the Giants, this formula assumes that both Osi Umenyiora and Michael Strahan will be missing. If Strahan returns, their score should improve.

Defensive Line Rankings- A New Ranking System

As has been asserted here several times, line play in the NFL is vital. Many people have said for a long time that games are won and lost on the offensive and defensive lines. Well, it's rarely that simple, but it is true that how good your line is will certainly go a long way in predicting how good your team will be.

The Football Know It All has developed a system using three categories to determine the quality of a defensive line. Today, I will lay out the criteria and list the defensive line rankings of each team for 2007. In my next post, I will take into account acquisitions, key losses, aging, and draft picks to give a best estimate for how the defensive lines will perform in 2008.

The new defensive line rating will be called Defensive Line Index (DLI). The three categories that make up DLI are:

1. Sacks- I wish that QB pressures was an official stat, because I believe that it is a fairly more accurate assessment of how much pressure a D-line puts on a quarterback. However, sacks are still a good measure of how much pressure a D-Line exerts on quarterbacks. Furthermore, teams that sack the quarterback a lot give up fewer points and win more games. There is a 0.55 correlation between the number of wins a team has and its sack total. The top five teams in sacks in 2007 all made the playoffs, and the top 2 teams faced off against each other in the Super Bowl.

2. Rushing yards/carry in the first half- Why only look at rushing yards in the first half? Because in the first half, all offenses are trying to score points, whereas in the second half, teams with big leads simply run more and try to eat up time. This leads to lower yards/carry. Thus, teams that are often behind in the second half give up fewer yards/carry in the second half, because the run is more predictably coming. This phenomenon helps them put up better run defense numbers than they deserve. Incidentally, yards/carry allowed in the first half has a -0.31 correlation with wins, whereas overall yards/carry allowed only has a -0.08 correlation. Clearly, First Half Yard/carry is the better index.

3. Percentage of tackles by D-Line- The better the D-Line, the more often it will tackle the ball carrier. Lesser D-Lines miss more tackles and depend more on linebackers and defensive backs to tackle ball carriers. % D-Line Tackles had a 0.23 correlation with winning percentage.


Using these three criteria, I used a regression for each category relative to its relationship to win percentage and adjusted weights in order to account for the differing numerical values of different categories. Below are the results for the 2007 rankings for DLI. The average score was 27.4, with a standard deviation of 7.0:

1. New York Giants- 44.5
2. Seattle Seahawks- 38.9
3. Minnesota Vikings- 37.6
4. Dallas Cowboys- 37.0
5. San Diego Chargers- 35.9
6. Baltimore Ravens- 34.4
7. Tampa Bay Buccaneers- 33.4
8. Green Bay Packers- 32.2
9. Philadelphia Eagles- 31.7
10. New England Patriots- 31.2
11. Chicago Bears- 28.3
12. Tennessee Titans- 28.1
13. Washington- 27.9
14. New Orleans Saints- 27.8
15. Jacksonville Jaguars- 27.4
16. Kansas City Chiefs- 25.8
17. Houston Texans- 25.3
17. San Francisco 49ers- 25.3
19. Detroit Lions- 25.1
20. Pittsburgh Steelers- 24.9
21. Indianapolis Colts- 24.8
22. Arizona Cardinals- 24.7
23. Carolina Panthers- 23.8
24. St. Louis Rams- 23.4
25. Miami Dolphins- 22.8
26. Denver Broncos- 22.2
27. New York Jets- 20.8
28. Buffalo Bills- 20.6
29. Cleveland Browns- 20.1
30. Cincinnati Bengals- 16.8
31. Oakland Raiders- 15.4
32. Atlanta Falcons- 14.4

The DLI, by the way, has a very strong correlation of 0.50 with winning percentage and a correlation of -0.52 with points allowed. These correlations demonstrate that DLI has high predictive validity as a predictor of overall defensive and team performance.

How Running Back Tandems Help Win Games

One truth that has been uncovered by the Football Know it All is that great running backs really distinguish themselves in the 4th quarter. In the first three quarters of a game, there is less variance in yards per carry, but in the fourth quarter, elite running backs like LaDainian Tomlinson and Adrian Peterson really pull away from the pack.

The ability to run the ball late in the game is a key determinant not only in who are the great running backs. Yards per carry in the fourth quarter is also one of the strongest predictors of which team will win a Close Game, previously defined as a game decided by 8 points or less. There is another stat that is important to predict the outcome of games. Team yards per carry after the 20th carry of the game have a 0.32 correlation with the overall outcome of the game. A 0.32 correlation indicates that while there are certainly other factors, yards/carry after the 20th carry have a significant impact on the game's outcome.

Only 3 running backs averaged more than 20 carries per game last year, however. So, in order for a team to enjoy this advantage, they must have a potent running back tandem. Teams that have a second running back who had over 300 yards rushing and averaged over 4.0 yards per carry enjoyed the late-game running advantage and had the inside track on winning close games. Below is a list of #2 running backs who helped their teams by gaining 300 yards rushing and averaged 4.0 yards per carry. The backs in bold backed up running backs who also average 4.0 yards per carry:

Jerious Norwood- Atlanta Falcons
Fred Jackson- Buffalo Bills
DeAngelo Williams- Carolina Panthers
Travis Henry- Denver Broncos (released)
TJ Duckett- Detroit lions
Indianaplois Colts- Kenton Keith
Maurice Jones-Drew- Jacksonville Jaguars
Jesse Chatman- Miami Dolphins (now on Jets)
Chester Taylor- Minnesota Vikings
Sammy Morris- New England Patriots
Derrick Ward- New York Giants
Leon Washington- New York Jets
Correl Buckhalter- Philadelphia Eagles
Najeh Davenport- Pittsburgh Steelers
Michael Turner- San Diego Chargers (now on Falcons)
Maurice Morris- Seattle Seahawks
Chris Brown- Tennessee Titans (now with Texans)

As you can see, running back tandems have become the norm in the NFL. Moreover, it has become increasingly common for team to use a draft pick in the first three rounds on a running back, even when they already have an elite back on the roster. This trend demonstrates that smart teams are investing in running back pairs. Even in their rookie years, strong backs who work in tandem with another strong back have seen their teams increase their win totals by three or more games. Recent examples in just the last three years are:

1. New Orleans Saints
2. Minnesota Vikings
3. New York Jets
4. Tennessee Titans
5. Jacksonville Jaguars
6. Miami Dolphins

Expecting a rookie to be your lone feature back has not worked, however. Teams seem to have only benefited immediately with drafting a running back when there is another start back in place with which to team. Below are the high-drafted rookies who will join established stars in the backfield:

Darren McFadden- 4th overall pick- Oakland Raiders
Jonathan Stewart- 13th pick- Carolina Panthers (DeShaun Foster no longer around; will team with Williams)
Felix Jones- 22nd overall- Dallas Cowboys
Rashard Mendenhall- 23rd overall- Pittsburgh Steelers
Ray Rice- 55th overall- Baltimore Ravens (as a side note, having seen Rice a lot, I see a lot of upside teaming him with McGahee)
Jacob Hester- 69th overall- San Diego Chargers
Steve Slaton- 89th overall (will team with Chris Brown and Ahman Green)

Ranking NFL Quarterbacks- A More Accurate Passer Rating

Before I delve into adjusting passer rating, one issue needs to be cleared up. The QB rating system, as it stands now, is not that bad. True, there can be some adjustments, two of which I will make in this post, but overall, the QB rating fairly accurately measures a quarterback's performance.

I hear pundits and commentators laugh and sneer all the time about the rating, because it requires some convoluted formula that few people understand. Well, if they were to look at the actual criteria that make up the quarterback rating instead of loking for something to complain about, maybe they wouldn't always be so quick to complain. The QB rating in the NFL is based on four different categories:

1. Completion percentage
2. Touchdown rate
3. Interception rate
4. Yards per attempt

Are any of those four categories unreasonable? Are there better categories for getting to the core of what a quarterback is supposed to do? I dunno, these four categories seem pretty sensible to me. Plus, the reason that the formula is so complicated is because the four categories produce very different numbers that cannot simply be added up. Sophisticated weighted scales and formulas must be constructed in order to give all categories equal weight.

A final defense of QB rating before I make my moderate adjustments to it: Look at the top ten QB's in passer rating in 2007:

1. Tom Brady- 117.2
2. Ben Roethlisberger- 104.1
3. David Garrard- 102.2
4. Peyton Manning- 98.0
5. Tony Romo- 97.4
6. Brett Favre- 95.7
7. Jeff Garcia- 94.6
8. Matt Hasselbeck- 91.4
9. Donovan McNabb- 89.9
10. Kurt Warner- 89.8

Now, you may have some slight qualms with a name on the list here and there, but one would be hard-pressed to argue that this list was not a pretty good reflection of QB performance in 2007.

That said, there are a couple of adjustments that can be made to make the list a little more representative of QB performance. There are three factors I see that the QB does not control that get factored into QB rating:

1. Dropped passes by the receivers lower a quarterback's completion percentage.
2. Yards after catch by a receiver give the quarterback extra yards per attempt.
3. Sacks affect the quarterback in numerous ways.

As for sacks, some of them are his fault, while others are the offensive line's fault. I will try to figure out how to distinguish between these better, but as of now, I do not have a good strategy. Therefore, I will not address sacks now.

I will address YAC and Dropped Passes. I will factor out the YAC from Yards per Attempt and factor out Dropped Passes from Completion Percentage to come to what I called QB Rating Plus. Below are the 2007 rankings for QB Rating Plus:
Rating Rating Plus
BUF Edwards 70.4 69.4
MIA Lemon 71.0 70.6
NYJ Clemens 60.9 59.4
NE Brady 117.2 116.9
IND Manning 98.0 99.7
TEN Young 71.1 70.8
HOU Schaub 87.2 86.1
JAC Garrard 102.2 102.7
CLE Anderson 82.5 83.7
PIT Roethlisberger 104.1 104.0
BAL Boller 75.2 75.6
CIN Palmer 86.7 86.1
KC Huard 76.8 77.5
SD Rivers 82.4 81.1
OAK McCown 69.4 69.7
DEN Cutler 88.1 87.5
NYG Manning 73.9 76.8
DAL Romo 97.4 97.0
PHI McNabb 89.9 89.5
WAS Campbell 77.6 78.6
TB Garcia 94.6 96.1
NO Brees 89.4 90.1
ATL Harrington 77.2 78.2
CAR Testaverde 65.8 67.7
DET Kitna 80.9 81.3
CHI Griese 75.6 78.4
GB Favre 95.7 93.0
MIN Jackson 70.8 71.8
SEA Hasselbeck 91.4 90.4
SF Dilfer 55.1 58.6
ARI Warner 89.8 90.2
STL Bulger 70.3 71.8

As you can see, the differences are not tremendous, but for several quarterbacks, the changes alter the rating enough to changes their ranking in passer rating by several spots. The biggest winners under the new system are: Eli Manning, Peyton Manning, Jeff Garcia, Brian Griese, Mark Bulger, Vinny Testaverde

The biggest losers under the new system are: Brett Favre, Kellen Clemens, Philip Rivers.

During the 2008 season, I will be studying sacks. I believe that this will provide the best improvement yet in measuring quarterback performance.

Last Year's Close Games Can Help Predict This Season's Records

In one of the Football Know It All's earliest posts, I discussed how year-to-year records have a faily weak correlation. One of the reasons for this is parity in the league. Turth be told, aside from the elite five or six teams and the five or sixe teams residing at the the bottom of the NFL barrel, there is not a tremendous amount of variance between the rest of the NFL teams.

This relative equality in the NFL leads to a large amount of Close Games, defined as games decided by 8 points or less. In fact, over the past five seasons, 48%, or roughly half, of the NFL's regular season's games have been Close Games. What decides the outcomes of these close games? There are many factors, and in fact, in my next post, I will talk about the kind of running game that helps teams tremendously in close games.

One factor, however, is random events. When teams are within a few points of each other, a number of factors, from a gust of wind, a penalty, or a dropped pass can affect the outcome. Supporting this assertion is that the standard deviation between NFL teams is significantly greater for overall record than for record in Close Games. This figure implies that in Close Games, the difference in the teams' qualities starts becoming less important while the impact of chance creeps in.

These things make victims of even the best teams in football. For instance, the Colts have had a 79% winning percentage over the past five seasons. However, in Close Games in that time, their winning pecetnage has been only 63%. Now, 63% is still very good, but it is substantially worse than 79%. One thing that happens is that, when they let teams stay close late into a game, they allow for the possibility of random events having more of an impact. The mark of good teams, however, has been that they rarely allow inferior teams to close in and make it a game.

The thrust of all of these figures is that random events do play a role in the outcomes of close games. An interesting notion to consider is that almost all teams play between 7-9 Close Games per year. So, each year, the random events that occur in close games can have a small, yet noticeable, impact on a team's record. As we've mentioned before, random events even out over time. It has been demonstrated that a team that loses a disproportionate number of Close Games one year will often improve in its Close Games record, and often in its record overall.

Thus, teams that lost a disproportionate amount of Close Games in 2007 may, by the simple power of probabilities, see an improvement this year. To keep an eye on this trend, here are a collection of teams that lost a large percentage of Close Games last year:

Pittsburgh Steelers
San Diego Chargers
Indianapolis Colts
Minnesota Vikings
Seattle Seahawks

Some teams that fared better in Close Games than they did overall and thus may not fare as well this year include:

Carolina Panthers
Denver Broncos
Buffalo Bills
Tennessee Titans
San Francisco 49ers

Remember, though- Just because random events take more of a role in close games does not mean that they are the sole predictors. Far from it. Even in close games, the odds still overwhelmingly favor the teams that are designed to win such games. Next post, I'll discuss what type of running game is needed to improve a team's chances in close games.

Age and Defensive Performance

A quick post today...

Today we take on two pieces of conventional wisdom about how age affects defensive performance.

Conventional Wisdom #1: While you want veteran leadership, you don't wasn't a defense to be too old. After all, older players will get injured, and they get worn out by the end of the season.

The truth: Actually, there is a very strong correlation between age and a defense's performance. Namely, the older the defensive unit, the better the defense performs over the course of the entire season. This truth holds even when taking injuries into account. In fact, there is no relationship between how old a defensive player is and how many games he will miss in a season due to injury.

NFL defensive schemes are a complex thing to learn, and some gray hairs among the defensive unit are clearly a good thing, not a bad thing. So, if your team had upgraded on defense but you worry about the new acquisition's age, relax. The odds are likely that he will do more good than harm.

Conventional Wisdom #2: Penalties are a killer, and younger, less disciplined players are more likely to commit them.

The truth: Well, for starters, defensive penalties are not a killer. There is no relationship between the amount of penalties a defense commits and its defensive ranking. Nor is there a relationship between defensive penalties and the amount of points a defense allows. While a penalty in any particular game can obviously change the course of a game, over the course of a season, a defense will not be harmed if it is prone to penalties.

The second point to make about this addresses age and penalties. You often hear commentators calling penalties, "rookie mistakes." You also hear them mention how as a player matures, he will smarten up and stop making so many penalties. Well, according to statistics, this is nonsense. When it comes to committing a lot of penalties, it appears that players are who they are. There is zero statistical decline in a player's penalty rate as his career progresses. Furthermore, there is no relationship between years of NFL experience and the amount of penalties that a player gets.

Which Stadiums Give Their Teams the Best Home-Field Advantage

We usually assume that home field gives the host team a distinct advantage over the road team. In fact, announcers will usually talk about the disadvantage that a team has because they have to go on the road to play. However, when you look at the evidence, not every home field gives its team an advantage. Consider this:

1. There is no correlation overall from year to year for home records. In other words, many teams in the NFL that performed 3 games better at home than on the road one year, for instance, fare no better at home than on the road the next year.

2. When comparing each team's home record against each team's road record, there were 10 teams for which there was no statistical difference whatsoever. Those 10 teams, in other words, performed just as well on the road as they did at home. In fact, there are four NFL teams that actually perform better on the road than they do at home over the past five years!

Okay, so those points made, the are an additional handful of teams that over the past five years have enjoyed a consistent, moderate homefield advantage. Finally, there are an additional dozen or so teams that perform so much better at home than they do on the road, that these teams are considered to have the best homefield advantage in all of the NFL.

When trying to pick the outcome of a close matchup and you want to take homefield advantage into account, it may be wise to consult the table below. As you'll see, not all teams enjoy the same advantage at home. Let's break down the list and try to examine why some stadiums help their teams more than others.

First, here are the teams for which their home field does not help them at all. The number in parentheses in the margin by which their winning percentage at home is better than their winning percentage on the road:

Carolina Panthers= -10
New Orleans Saints= -8
New York Giants= -3
Philadelphia Eagles= -3
Tennessee Titans= 5
New England Patriots= 5
Dallas Cowboys= 5
Atlanta Falcons= 5
Indianapolis Colts= 8
Green Bay Packers= 8

A few observations:

1. As my wife actually pointed out, the Giants and Eagles being on this list is not surprising. I live in New York and she lived in Philly for four years, and fans of those two teams are, shall I say, brutal to their teams. Maybe this shows that constantly berating your own team may just have a negative impact on their performance.

2. New England and Indy also are not a surprise. Over the past 5 years, they've won so consistently on the road that their home record simply had little room to be much better.

3. Two myths shattered in one list- The Saints actually play worse in the Superdome than they do on the road. Plus, the vaunted Lambeau Field gives the Packers absolutely no discernible advantage over their visitors. Go figure.

4. Carolina fans, care to weigh in with a theory?

Next, the following teams enjoy a moderate advantage playing in their own stadium:

Miami Dolphins= 10
Washington Redskins= 13
San Diego Chargers= 15
Cincinnati Bengals= 15
Oakland Raiders= 18
Cleveland Browns= 18
St. Louis Rams= 18
Tampa Bay Buccaneers= 20
New York Jets= 20
Buffalo Bills= 20
Pittsburgh Steelers= 20

Observations...

1. Weather and geography, at first glance, don't appear to play much of a factor. There are just as many warm weather teams on the list as there are cold weather teams, and they seem to be spread around the country.

2. The Jets, who play in the same stadium as the Giants, enjoy a significant advantage at home, while the Giants are actually worse. In my opinion, it's always been clear that Jets fans have been more loyal than Giants fans (probably because they have to be). But can that really be the sole explanation? I'm open for suggestions.

3. The Redskins are the only NFC East team that actually has a homefield advantage. I'm not sure if I should make anything of that, or if it's simply weird.

Finally, here are the teams with a tremendous homefield advantage. Before looking, do you think you can guess #1?

Houston Texans= 23
San Francisco 49ers= 23
Denver Broncos= 23
Jacksonville Jaguars= 23
Detroit Lions= 25
Chicago Bears= 25
Kansas City Chiefs= 28
Minnesota Vikings= 28
Arizona Cardinals= 35
Seattle Seahawks= 38
Baltimore Ravens= 43



Observations...

1. First of all, just astonishment at that number by the Ravens. Playing with a winning percentage 43 points better at home than on the road, they are like two completely different teams.

2. Something Seahawks fans already know- As the playoff race gets tight, they must keep an eye on home and away game left, because at home they are excellent. On the road, they're not even in the top half of NFL teams.

3. I've read many times about how loud and unfriendly Arrowhead can be for visitors. Now I see empirical proof of it.

4. Now we know what it will take to turn around the Cardinals- more home games.