Tuesday, March 6, 2018
Do Tackle Statistics Matter?
For years, I have preached skepticism about the NFL's tackle statistics. The figures aren't even consistent — they vary depending on your source. Football historian John Turney has written about this, outlining the way tackle statistics differ according to the NFL (which uses tallies compiled by coaching staffs), sites including ESPN.com and Pro Football Reference (which use play-by-play statistics from official gamebooks), and Pro Football Focus (which does its own funky math). My focus here will be on the official NFL totals, the ones from coaches.
About a decade ago, Rick Gosselin of The Dallas Morning News "surveyed a handful of NFL head coaches" and determined that they felt 1.44 tackles per play was a legitimate average, given that many tackles are made by multiple defenders simultaneously. Gosselin himself preferred a number closer to 1.3. I would link to his piece, but the link I used is dead and I can't find a new one.
Anyway, the NFL uses three separate tackle stats: "Comb", "Total", and "Ast". The "Total" column are solo tackles or plays on which a defender was the primary tackler. "Assists" are — in theory — plays on which a defender was not the primary tackler but did assist in bringing the ball-carrier down. The "Combined" column, the default stat used for sorting and citing individual totals, simply adds the "Total" and "Assist" figures. It's reasonably straightforward.
Last season, there were 24,255 plays on which at least one player was credited with a tackle, 758 per team. According to the official stats at NFL.com, there were 752 "Total" tackles per team and 273 "Assists" per team, for a "Combined" average of 1,026 (due to rounding). That's 1.35 tackles per play, pretty close to Gosselin's dream number.
But there's a huge discrepancy from team to team. Take "Total" tackles, which you'd expect to be relatively straightforward. The Los Angeles Chargers defense was credited with 831, despite just 756 defensive plays that resulted in tackles. That's 9.9% inflation. Conversely, the Indianapolis Colts had just 689 tackles on 782 such plays, just 88.1% of their expected total. Nine teams finished more than one standard deviation off the league average of 99.2 Total tackles per 100 defensive plays that resulted in tackles. The Colts, Panthers, Falcons, and Bengals all finished below 94/100, while the Chargers, Giants, Cardinals, Patriots, and Buccaneers all finished above 104.5/100.
That's nothing compared to Assists. The Cincinnati Bengals were credited with 346 assisted tackles, almost 75% more than the Arizona Cardinals (198). These teams played the same number of games! On average, teams have 36.3 Assists per 100 Total tackles. A quarter of the league, though, averages less than 30, highlighted by Arizona's mere 25.2%. The Bengals aren't even the most extreme team on the other side. The Panthers had 637 Total and 322 Assisted tackles — 50.5 Assists per Total, more than twice as many as Arizona. That both figures are credible is not plausible. Whatever else you take away from this column, I implore you: don't believe in the NFL's Assist statistic.
It's common for star players to get Assists on any play they were near the ball-carrier. In 2017, Luke Kuechly was credited with 74 Total tackles and 51 Assists. That's almost 70 Assists per 100 Total; I'll remind you that the league average is 36. It makes sense for a middle linebacker to have higher-than-normal Assist totals, but not that much higher. Seattle's Bobby Wagner had 97 Total and 36 Assist, almost exactly the league average, and he plays the same position as Kuechly, but without coaches padding his stats.
The "Combined" category that the NFL promotes as the most important adds Total and Assist stats, weighted equally, so an Assist is just as good as a solo tackle. In 2017, teams averaged 1,026, just over 1.35 per plays on which at least one player was credited with a tackle. The Chargers, Giants, Washington, Buffalo, and Houston all had more than 1.40 Combined tackles per play, while Kansas City, Chicago, and Baltimore all had fewer than 1.30.
Some teams are stingy with Total but generous with Assists, like the Colts, Panthers, and Bengals. Others are generous with Total, but dole out Assists sparingly, like the Cardinals, Patriots, and Buccaneers. Most teams are close to average, of course. Then there are the New York Giants.
The Giants awarded 107 Total and 41 Assisted tackles for every 100 plays on which an opponent was tackled, both figures significantly above average. This team, which went 3-13, led the NFL in Combined tackles (1,157). Which team had the fewest? The Super Bowl champion Philadelphia Eagles, with just 935. According to the league, the worst team in the NFC had the most tackles, and the best team had the fewest. Keep that in mind next time you want to cite tackles as an important stat!
There are good reasons for bad teams to make more tackles. Their defenses are on the field for more plays, since they allow long drives and their offenses usually punt or turn the ball over. There are other variables, too. An aggressive defense will make fewer tackles, since possessions quickly turn into touchdowns or takeaways, while a bend-don't-break defense will generate many tackles. Tackles in the middle of the field usually result in Assists, while tackles by pass rushers and defensive backs are more likely to be solo tackles. Generally, though, the best teams make fewer tackles. Eight of the nine lowest "Comb" totals in 2017 belonged to playoff teams, and the exception, the Denver Broncos, had a very good defense. Eleven of the top 12 teams, meanwhile, missed the postseason.
What this means is that players on bad teams have artificially inflated tackle totals, even before any of the shady ways the Assist category can be tabulated. Let's look at last year's top 10 in Comb:
t1. Preston Brown, BUF — 144
t1. Blake Martinez, GB — 144
t1. Joe Schobert, CLE — 144
t4. Deion Jones, ATL — 138
t4. Christian Kirksey, CLE — 138
6. Demario Davis, NYJ — 135
7. Bobby Wagner, SEA — 133
8. C.J. Mosley, BAL — 132
9. Zach Brown, WAS — 127
10. Luke Kuechly, CAR — 125
Are Preston Brown, Blake Martinez, and Joe Schobert guys who come to mind as elite players? This is why it's so frustrating that the NFL uses Comb rather than Total as its primary tackling stat, never mind the issue with relying on coaches rather than game books. Brown had the most outrageous Total-to-Assist ratio in the league last season, 84-to-60. Forget 36.3 Assists per 100 Total, that's 71.4 per 100. It's not merely absurd, it's disrespectful to other players and insulting to fans. Martinez and Schobert also had very high Assist totals.
This just is not a useful stat. Solo tackles are hard to fake. Some teams will generously credit a Total when an Assist might be more appropriate, but at least the guy was involved in the play. The Bills' coaching staff gave Preston Brown an Assist any time he was within five feet of the play. Ray Lewis used to jump onto piles after the runner was down and get credited with Assists. Players are still doing that.
There are a lot of potential issues with treating tackle stats as meaningful, but the main one, the most important, is not to use Assists or Combined tackles: stick to Total, the one that's hardest to fake. Some of the issues identified here still apply, but the game books used at sites likes Pro Football Reference are more reliable than the NFL's official totals, as well..