YAC may be a Quarterbacking Skill

by Denis O'Regan

The distance a completed pass travels in the air would appear to be a significant factor in how much YAC a pass is going to generate. A flat pass to a running back is likely to have more potential YAC than a longish sideline pass where the defense has more time to converge around the potential receiver. Therefore, I regressed the average length of a QB's completion (his air yards), against the amount of YAC he generated. I used all QBs from 2006-2010 who had been their teams primary starter.

Air yards were statistically significant as an indicator and the correlation was just over 0.16.

The amount of YAC was given by 6.83 minus (air yards*0.296).

Next I in turn removed each player from the regression repeated the process and calculated his expected YAC from his actual length of completion using the new regression. I then subtracted each QB's actual YAC from his expected YAC to find which players had produced more YAC than expected given their air yards. The players with more than their expected YAC over the five seasons of the data are listed below.

Best quarterbacks for generating YAC after accounting for depth of completion.

QB	Expected YAC	Actual YAC	Difference
D.McNabb	4.87	5.82	0.95
T.Romo	4.72	5.44	0.72
P Rivers	4.7	5.4	0.7
M Stafford	5.24	5.92	0.68
A Rodgers	4.72	5.25	0.53
G Frerotte	4.82	5.34	0.52
M Vick	4.59	5.02	0.42
T Brady	4.95	5.36	0.41
J Campbell	5.24	5.65	0.41
M Schaub	4.81	5.15	0.34
K Orton	4.98	5.31	0.34
M Cassel	5.08	5.42	0.34
B Favre	5.1	5.38	0.28
J Flacco	4.9	5.15	0.25
A Smith	5.21	5.46	0.25
M Sanchez	4.7	4.91	0.21
B Roethlisberger	4.56	4.76	0.2
J Cutler	4.83	5.03	0.2

With the exception of a few low sample size interlopers, the list contains a very impressive list of QBs, including 8 of this season's post season ones.

The next table contains the largest underperformers, players whose actual YAC was much less than the figure predicted by combining the regression with the actual distance their completions travelled through the air.

Worst quarterbacks for generating YAC after accounting for depth of completion.

QB	Expected YAC	Actual YAC	Difference
K Boller	4.73	3.3	-1.43
B Croyle	5.21	4.17	-1.04
A Walter	4.49	3.52	-0.97
S McNair	4.96	4.02	-0.94
C Frye	5.21	4.28	-0.93
B Gradkowski	5.38	4.49	-0.89
S Rosenfels	4.76	4.03	-0.73
R Fitzpatrick	4.99	4.3	-0.7
C Henne	4.91	4.26	-0.65
C Pennington	4.9	4.26	-0.64
D Carr	5.6	5.01	-0.59
K Collins	4.74	4.19	-0.55
B Quinn	5.35	4.84	-0.51
M Bulger	4.83	4.33	-0.5

Very much a mix of poor players or good ones declining at the tail end of their careers. There are some better players due up fairly soon on this part of the list, most notably Peyton Manning, but they're still outnumbered by poorer ones. Manning is probably an unusual outlier as he's been the most accurate QB bar non when you allow for the distance he throws. His YAC's probably dragged down disproportionately because he is so deep and so accurate.

So to summarize, QBs who get more yards after the catch than you would expect them to get when you allow for the depth of their completions tend to be elite players. Those who underperform compared to their peers tend not to be generally regarded as very good QBs.

This may mean that gaining YAC is at least partly attributable to a quarterbacking talent. McNabb was above average compared to his expected YAC at both Washington and Philly, his numbers aren't dependent upon a good performance at Philly alone. While Baltimore were massively below average with McNair and Boller, but above average with Flacco.

A quick note on the correlation of the original equation. It's not strong, but there must be a heck of alot of noise and it does jump significantly if you restrict the sample to just good or just bad YAC QBs.