TCU has played much better in the second half of games this year. What other schools have seen dramatic shifts of play after halftime?
10 Aug 2010
by Bill Barnwell
For those of you who haven't seen it, please read last week's introduction of YAC+ before getting to this article.
In this follow-up, I want to take a look at what YAC+ says about the player pool as a whole. Is YAC+ a reliable, consistent statistic? Is it subject to massive year-to-year swings? I'll identify a few players and what their stats say about these relationships along the way.
Let's start with the year-to-year consistency of YAC+. Anecdotally, it would make sense that the players we introduced as having elite YAC skills in our last article -- Darren Sproles and Miles Austin -- would have those sort of skills from year-to-year. We noted that Sproles would have led the league in YAC+ per catch in 2008 if he'd qualified with one more catch -- but, on the other hand, he was below-average in 2007. Austin only had a combined 18 catches in 2007-08, which makes that data pretty useless, but he was below-average in 2007 and above-average in 2008.
For a league-wide check, we measured the year-to-year correlation of YAC+ per catch for players with 30 or more catches in consecutive seasons. I also split the groups out by position, to see if one particular group was more or less consistent than another. Obviously, the fact that there are only four years of data to draw upon limits the predicative value of these stats, but there are still some really interesting things to discuss here. The table below reports those year-to-year correlations, with the sample sizes in parentheses.
|Table 1: Year-to-Year YAC+ Per Catch Correlation|
|All Receivers||0.44 (85)||0.17 (84)||0.38 (90)|
|RB||-0.03 (11)||0.00 (11)||-0.38 (14)|
|WR||0.38 (54)||0.17 (55)||0.36 (55)|
|TE||0.23 (17)||-0.41 (18)||0.32 (21)|
Well, that's not what I was expecting. The year-to-year YAC+ correlation ranges from fairly weak (2006-07, 2008-09) to just about useless (2007-08). Sadly, we're about five years away from figuring out whether 2007-08 was the outlier, but what a strange dip in reliability!
During that season, tight end YAC+ totally flipped, which is worth exploring. The 2007 leader for YAC+ per catch was Donald Lee (1.2); Lee promptly fell off to -2.2 YAC+ per catch in 2008, and after being replaced by Jermichael Finley, was at -1.9 in 2009. Just behind him was Desmond Clark (1.0), who also fell below-average a year later (-0.2). On the other side of things, David Martin had a dismal -2.2 YAC+ per catch in 2007, and a year later, he was almost exactly average (0.02). Vernon Davis was the next-worst, at -1.1 YAC+ per catch, and he improved to 1.1 YAC+ in 2008, although he dropped back down to -0.5 YAC+ per catch in 2009.
The consistency of wide receiver YAC+ also fell off in a much larger sample, though, and there are a few players to note there. The league leader in YAC+ in 2007 was Greg Jennings, who put up a very impressive 3.3 YAC+ per catch. Jennings' YAC+ progression over the past four seasons: 3.0, 3.3, -0.1, 2.4. Perhaps Packers fans can help us identify a specific factor that led to the YAC decline in 2008. Obviously, Green Bay changed quarterbacks that year, but did it really affect Jennings differently from other players? As for injuries, Jennings suffered a rib injury and a concussion in 2008, but he had ankle and groin injuries in 2007 that would theoretically cost him more in terms of running after a catch.
Jennings wasn't the only one who saw a swift downturn. There were four other qualifying receivers who had YAC+ per catch above 1.0 in 2007. One -- Patrick Crayton -- retained his YAC+ rate, going from 1.6 in 2007 to 1.5 in 2008. The other three all fell way off: Roddy White (1.3 YAC+ per catch in 2007 to -0.2 in 2008), Reggie Williams (1.9 YAC+ in 2007, -1.8 in 2008), and Anthony Gonzalez (1.6 YAC+ in 2007 to -0.7 YAC+ in 2008).
The trend wasn't as pronounced on the other side of the coin. 16 receivers had a YAC+ per catch below -1.0 that year, paced by Bryant Johnson, who had a YAC+ of -1.9 in 2007. Only five of these receivers produced a positive YAC+ figure in 2008.
Contained in that group of 16 players is a familiar lightning rod for our criticism. Chris Chambers has been, arguably, the most consistently below-average producer of YAC of any receiver in football. His YAC+ figures from 2006 to 2009 go -1.3, -1.7, -2.2, and -0.3. Remember -- this isn't attempt-based, so it doesn't account for Chambers' poor catch rate. It's strictly based on what he does after he's caught the ball.
On the other hand, consider a player with a style similar to Chambers, Vincent Jackson. Obviously, Jackson is a much better player, but his YAC+ figures have also been disappointing: -1.2 in 2007, -1.0 in 2008, and -1.3 a year ago. This led me to wonder whether YAC+ is too harsh on players who catch jump balls, such as Chambers and Jackson. Then I considered a third sort of player who gets those kind of passes, Calvin Johnson. He's had a positive YAC+ in 2008 (1.8) and 2009 (0.7). So the answer is: I don't know what it all means.
Although it's a very small sample size in each season, running backs have exhibited virtually no year-to-year YAC+ consistency. In 2006, the YAC+ leader among backs was Larry Johnson (3.6 YAC+ per catch); a year later, he was exactly league-average, and he hasn't qualified for the leaderboard since. Behind him was Mewelde Moore (3.1), who didn't qualify again until 2008, when he was at 0.2 as a member of the Steelers. Maurice Jones-Drew (2.5) was in fourth in 2006, and he's one of the few backs who has been relatively consistent in YAC+, with a figure of 2.8 in 2007, 2.0 in 2008, and then a slightly above-average total of 0.3 in 2009. That 2.8 total in 2007 was tied for the league lead with Ronnie Brown, who promptly fell off to -0.7 YAC+ in 2008.
What happened to the leaders of 2008 in 2009, though? Well, several players with impressive YAC+ figures didn't qualify a year later, including J.J. Arrington, Darren McFadden, Jerious Norwood, and Derrick Ward. Steven Jackson, who was in second place in YAC+ in 2008, fell slightly below-average in 2009. Chris Johnson, who was tied for the worst YAC+ among running backs in 2008 (-0.7, alongside Brown), had the second-best YAC+ amongst all players in 2009. I think the small sample size certainly complicates things, but I don't think it's possible to make a case that gaining above-average YAC is a consistent skill for running backs.
Other interesting notes from the past four years:
We'll finish off our series on YAC+ later this week with a look at quarterback YAC+.
16 comments, Last at 19 Aug 2010, 1:55pm by MR