TCU has played much better in the second half of games this year. What other schools have seen dramatic shifts of play after halftime?
27 Aug 2010
by Bill Barnwell
As previously promised, it's time to take a look at the impact of quarterbacks on yards after catch (henceforth YAC) using our new metric for analyzing a receiver's ability to run with the ball, YAC+. Although it's not realistic to separate entirely a quarterback's impact on YAC from a receiver's, we'll endeavor to find what sort of influence quarterbacks wield on YAC and how consistent that influence is from year to year.
Since the last YAC+ article was a laptop repair ago, I'll provide a quick refresher on how YAC+ works. For every completion, we calculate a baseline for expected YAC by looking at comparable passes from 2006-2009. We compare the actual YAC gained or lost on the play to the baseline. The resulting difference is YAC+. For more background on how YAC+ works, you can check out the first two articles on the topic here and here.
(For reference, the most YAC lost on one play in the four-year stretch is 10 yards. Brandon Marshall caught a pass thrown two yards behind the line of scrimmage from Jay Cutler on third-and-4 in 2007, promptly lost 10 additional yards, and fumbled in the process. That produced a YAC+ figure of -16.9, also the worst figure in the four-year period. )
First, let's check the leaderboard. Here are the top ten quarterback seasons from 2006 through 2009 by both raw YAC per completion (left side of the table) and YAC+ per completion (right side of the table), with a minimum of 100 completions in the given season to qualify.
|Table 1: YAC vs. YAC+|
What jumps out on those two top ten lists? For one, the groups are mostly the same, as only Mark Brunell and Philip Rivers fell out of the top 10 after switching from YAC to YAC+. The table includes two of the worst seasons by any quarterback over the timeframe, J.T. O'Sullivan's 2008 and Matthew Stafford's 2009. The only player who appears in the YAC+ top 10 twice is Donovan McNabb, and I've suggested that he struggled to hit receivers in stride during his time in Philadelphia.
The top season on that list is McNabb's from 2006. That was the year when the Eagles rallied to make the playoffs with a 5-0 finish under Jeff Garcia, who took over for an injured McNabb at the end of the year. The combination represents an example of one way to try and tease out the importance of a quarterback to YAC. Both McNabb and Garcia completed more than 100 passes on the year, one of 19 times in the past four seasons in which a team has seen two quarterbacks do just that. (Strangely, there were only two such teams in 2009: Buffalo and Tennessee.) While McNabb had the best YAC+ of the timeframe by more than a standard deviation, Garcia had a YAC+ of -0.9, the eighth-worst of any quarterback over the four-year stretch. Garcia was above-average in 2007 (0.5) and about average in 2008 (-0.1), which makes the huge disparity even stranger.
Of those 19 pairs, though, only seven of them had a difference in YAC+ that was greater than one standard deviation (.57). Some quarterbacks who look and play entirely differently -- like Kerry Collins and Vince Young in 2009 -- ended up with remarkably similar YAC+ figures.
If we look at the full four-year stretch (minimum: 400 completions), Tony Romo (.665 YAC+ per completion) just sneaks ahead of McNabb (.663). Also in the top five are Kyle Orton (0.5), Tom Brady (0.5), and Derek Anderson (0.4). On the flip side, Steve McNair has the worst YAC+ in the timeframe (-0.7), but remember that it's only considering 2006-07, not the earlier portion of his career. In the great statistical flukes category, Peyton Manning (-0.192) and Eli Manning (-0.195) are in a virtual dead heat during the past four years in this metric.
Guys like O'Sullivan, Stafford, and Anderson seem like they shouldn't belong in this conversation, but one thing they seem to have in common is that their work really came mostly in the course of one season. Stafford has only played one season so far, of course, while O'Sullivan had virtually all his attempts come during a stretch with the Niners in 2008, and Anderson had more than half of his completions (298, at a rate of 0.6 YAC+) come during the 2007 campaign. We need a much larger sample to say, but I suspect that these guys are just putting up an impressive YAC+ figure in a small sample and haven't been in the lineup enough for their statistics to regress to the mean.
The reason that comes to mind is because there's just not a whole lot of year-to-year consistency in YAC+ for quarterbacks. Among guys with 50 completions or more in consecutive seasons, the year-to-year correlation for YAC+ in 2006-07 was only 0.26. In 2007-08, it fell to 0.13, and in 2008-09, it was back up to 0.25. That's just not strong at all.
The sample size for those groups was either 26 or 27 quarterbacks in each season, which is still pretty limited considering we only have three sets of seasons to compare. In a trip to small sample size theatre, I went and looked at the 13 quarterbacks who had 100 completions or more in each season for the same team over the four-year stretch. Their year-to-year correlation was weak in 2006-07 (0.19) and 2007-08 (0.15), but in 2008-09, it jumped all the way up to 0.60! I don't think there's much to that figure, but it's worth mentioning considering how remarkably consistent league performance was as a whole between 2008 and 2009.
As much as I'd like to make the statement that quarterbacks simply don't have any effect on yards after catch, I don't think we have the data required to make that sort of statement as of yet. Furthermore, while it's certainly worth looking at going forward, I think YAC+ for receivers ends up being far more valuable than YAC+ for quarterbacks. The variance in receiver type is far greater than that of quarterbacks. Vincent Jackson and Wes Welker may have produced roughly similar DYAR figures last year, but they're obviously two dramatically different players stylistically. The difference between Philip Rivers and JaMarcus Russell might be great, but there's just not that much of a difference between Rivers and the fellow quarterbacks at his performance level when it comes to the types of routes he throws. Even the quirky throwing motion isn't as far off from other quarterbacks.
With all that on the books, it's time to put plus-minus and YAC+ on the shelf for the season. I'll re-visit the two statistics in Football Outsiders Almanac 2011. Let's just hope that it won't be a preview book for the UFL.
21 comments, Last at 30 Aug 2010, 12:40pm by Arkaein