You dare question PFF's top graders?
Another view of tackles is at Advanced Football Analytics:
http://www.advancedfootballanalytics.com/index.php/home/stats/defensive-players/cornerbacks
JJ is 13th overall in Tackle Factor -- which suggests he makes more tackles than would be expected out of your typical CB. This could be because the Rams pass defense is bad and allows more opportunities for JJ to make a tackle, or it could suggest that even though he might miss a lot of tackles, he's getting himself in position to have hell of a lot more opportunities to make a tackle than your typical CB.
I agree there's a lot more to evaluating tackling ability than the PFF limited view of just trying to count missed tackles -- but even so I think it is clear he needs to improve his tackling. Would love to read a story about how he's committing his offseason to fundamentals -- like tackling technique and not biting on the double move, etc.
This will give you a headache.
http://archive.advancedfootballanalytics.com/2010/03/tackle-factor.html
"Tackle Factor"
By Brian Burke
I keep seeing 49ers linebacker Patrick Willis' name listed at the top of defensive player statistics the last few years. He led the league in tackles in 2009 and 2007, and was second in 2008, but does this mean that Willis is really a top player?
Most fans understand that the tackle statistic is not a very good way to measure a defender. Weaker defenses tend to give up longer drives, giving players more opportunities to make tackles. So in a perverse way, more tackles can be a bad thing. If a defensive back has a lot of tackles, it may be because he's being thrown on successfully. Plus, certain positions get more tackles by the nature of team defense. Middle and inside linebackers will naturally have the most tackles by virtue of their role and where they are at the snap. If you scan down the list of the season leaders in tackles, you're likely to see a simple list of each team's central linebacker, assuming he was healthy most of the year. So how can we tell if Patrick Willis is really that good using just tackle information?
An Idea from Baseball
Baseball faced similar problems with defensive statistics. Until recent years, fielding skill was measured solely by the Fielding Percentage stat, which is a player’s number of put-outs and assists divided by his total of put-outs, assists, and errors. It’s basically a player’s “non-error rate.” This is a flawed way of looking at fielding for many reasons. For one thing, you can't make an error if you can't get to the ball.
In 1977 Bill James revolutionized fielding stats with the invention of Range Factor (RF). Say that for the major leagues as a whole, the shortstop position typically accounts for 20% of its team's putouts and assists. Assuming a relatively even distribution of fielding opportunities, a shortstop who creates significantly more than 20% of his team's outs could be considered to have better than average range and skill. And a shortstop who has significantly fewer than 20% could be considered to have below average range and skill. It’s elegantly simple and compellingly useful.
Tackle Factor
(I bet you know where I'm going with this.) What if we looked at the proportion of all 49ers tackles for which Patrick Willis was given credit? San Francisco logged a total of 832 tackles in the 2009 regular season, and Willis got credit for 114, a proportion of 13.7%. Willis is an ILB in a 3-4 scheme, and in 2009 the ILB position in all the NFL’s 3-4 schemes accounted for 21.5% of a team's tackle total. Because there are two ILBs on the field at once, a single ILB could be expected to average half that, or 10.7% of a team's total.
Willis' 13.7% compares very well with his position’s expected tackle rate. His ratio of tackle percentage compared to the expected percentage for his position is 13.7/10.7, or 1.23. In other words, Patrick Willis has a 'Tackle Factor' of 1.23; he makes 23% more tackles than you'd expect from his position, which tells us a lot about his ability to shed blocks, get to a ball carrier, and make a tackle.
To compare Willis to other players we can follow the same process. Redskins MLB London Fletcher notched 95 of Washington's 804 tackles in 15 games last season. Over a full season we could estimate he would have 16/15 * 95 = 101 'season-adjusted' tackles. Fletcher's adjusted share of the Redskin's tackles would be 101/804, or 12.6%. The MLB position in a 4-3 defense averages 11.9% of a team's tackles, making Fletcher's Tackle Factor 1.06.
Shortcomings
There are a number of shortcomings with TF. For starters, it tells us something very different about defensive backs than for linemen and linebackers. Just like total tackles, a weak pass defense would increase the proportion of tackles in the secondary. It still may tell us something about safeties, however. If a safety is making a very high proportion of his team’s tackles it may mean he’s a standout in an otherwise weak defense. We could also modify the stat to count only run plays, which might be even more illuminating.
TF penalizes players who are not every-down defenders. For now, it is adjusted for games played, but not for snaps on the field. Ideally, if we knew how many snaps each player was on the field we’d get a more reliable stat. Because so many players are not every-down defenders, the average TF is not 1.0. But on the other hand, if a player is not worthy of playing every down, that alone tells us something about his ability.
Baseball’s Range Factor suffers from many of the same issues, but it was nevertheless considered a quantum leap forward in defensive statistics. I think TF could also be a step forward despite its flaws. Defensive baseball stats have evolved significantly in the generation since RF was invented, and the concepts Bill James set forth underlie each new development.
I keep seeing 49ers linebacker Patrick Willis' name listed at the top of defensive player statistics the last few years. He led the league in tackles in 2009 and 2007, and was second in 2008, but does this mean that Willis is really a top player?
