27 Nov 2009
I wrote a post recently (that happily no one read) showing a seemingly strong correlation between how often a QB gets sacks and his numbers. Based off of seven QBs between 1.5 years, it seemed that there was a strong correlation between QBs moving to a new team and how an O-line affects that QB. However, even I realized the huge sample size problem. So I decided to actually extended that sample size to see how sacks affect a QBs performance. To determine this, first, I decided to see how often a QB gets sacked per every 100 passing attempts (S/100). Next, to extended the sample size. To do this I analyzed S/100 on Brett Favre. Favre has led all QBs in passing attempts and has had a long and illustrious career. Plus, I thought if I analyzed one QB and to make the QB performance independent as possible, the dtata would be clearer. So I analyzed how S/100 (again, sacks per 100 passing attempts) affects YPA, completion percentage, passer rating, and TD/INT ratio. Here's what I found:
After plotting out these numbers, I decided to find the R2 or the correlation. For those of you unaware of correlation, +1 means a strong positive correlation, -1 means a strong negative correlation, and 0 means no correlation. The R2 between S/100 and YPA is .002; between S/100 and Comp% is .0008; between S/100 and Passer Rating is .018; and between S/100 and TD/INT ratio is .018. These numbers are so small, that is laments terms, by looking at Favre's numbers, there is no correlation between S/100 and a QB's performance.
Disappointed, I decided to briefly look at Jay Cutler's short career. These numbers were drastically different. Again, there is very little correlation between S/100 and YPA and Passer Rating; however, there is a very strong correlation between S/100 and Comp% and Passer Rating. The R2 for Comp% is very strong for Cutler, being .453 and for TD/INT ratio being .225. There is a strong correlation for Comp% and a slightly strong correlation for TD/INT ratio.
Then I thought to myself, maybe looking at one QB wasn't the best idea. I want to see how sacks affect EVERY quarterback, not just one. So based on the Cutler and Favre numbers, I decided to look at every quarterback last year that had a minimum of 415 passing attempts and looked to see how S/100 affects YPA, Comp%, Passer Rating, and TD/INT ratio. Last year there were 21 QBs that fit this bill ranging from the very good Peyton Manning and Phillips Rivers to the crappy Marc Bulger and Kerry Collins. Here's what I found:
Again, I was disappointed. The R2 between S/100 and YPA is .125; between S/100 and Comp% is .049; between S/100 and Passer Rating is .162; and S/100 and TD/INT ratio is .172. The correlation is slightly stronger when analyzing all QBs as opposed to one, but the correlation is still fairly weak and essentially non-existent.
However, this research is not a total waste of time. Yes, overall, how often a QB gets sacked bears no relevance on how he performs. But that doesn't hold true on every individual QB. Some QBs, like Favre, it does not matter, and even on guys like Aaron Rodgers who gets sacked like crazy. However, on certain guys like Cutler, S/100 does not matter. And sometimes S/100 can show you how crappy certain guys are. Last year, Kerry Collins (min 415 attempts) had the 2nd least S/100, yet put up mediocre to awful numbers. So as a whole, S/100 shows no relevance, but on individual QBs, it may make a difference.
Now, I would love to be proven wrong. If someone finds a major flaw in my analysis or my work, please let me know. If someone had proven data to show how sacks do affect a QBs performance, I'd love to know about it, but until then, I don't think so.
To read the full post and see all graphs, go to:
5 replies , Last at 24 Feb 2010, 3:16pm by Spielman