Writers of Pro Football Prospectus 2008

25 Nov 2009

How Do Sacks Affect a QBs Performance?

I was recently thinking about the Matt Cassel trade and previous trade talks about him. The main reason Cutler wanted out of Denver is because Josh McDaniels actively went to get Cassel, even though he had a young QB coming off of a great year. Cassel getting traded forced him (obviously), Cutler, and Kyle Orton to change teams this year. Upon your basic knowledge of how the three QBs are doing this year, it seems that Cassel got overpaid and Denver got the better end of the trade and Chicago got screwed.

But I decided to look deeper. I, and I hope many fans of this site as well, know the great importance of an offensive line on a QB. It's easy to get off passes when no one is in your face and (as Bears fans like myself are all too familiar with this year), it's really hard to throw to your receiver with two guys breathing down your neck.

So I decided to look at Cutler, Orton, and Cassel. I calculated how many times they got sacked per 100 passing attempts (S/100) comparing last year's numbers to this years and here's what I found out.

Cassel (+2.66 S/100)
YPA: -1.2
Completion Percentage: -8.4
Passer Rating: -11.5
TD/INT ratio: +.09

Cutler (+1.79 S/100)
YPA: -0.7
Completion Percentage: -0.6
Passer Rating: -11.5
TD/INT ratio: -0.56

Orton (-1.41 S/100)
YPA: +0.6
Completion Percentage: +3.5
Passer Rating: +8.2
TD/INT ratio: +0.7

[NOTE: I realize my numbers may still be a bit confusing so I'll try to explain. +2.00 S/100 means that the QB is getting sacked two more times per every 100 passing attempts this season compared to last season. The numbers below like -1.0 Completion Percentage means that the QB is completing 1% less of this passes this year compared to his season last year]

It should be no shock or surprise that the more the QB is getting sacked, the worse of his numbers are and the less often he is getting sacked, the better his numbers are. The obvious outlier is Matt Cassel actually has a better TD/INT ratio this year, even though he is getting sacked more per every 100 passing attempts. I think that goes more towards the talent that Cassel has of what he's able to do that the effect of sacks itself.

Next, I decided to test this "theory" on other QBs who have recently changed teams. I analyzed Brett Favre's numbers on the Jets compared to his last season on the Packers, as well as his season on the Vikings compared to his season last year on the Jets. I also analyzed Chad Pennington's numbers during his 2008 Dolphins campaign compared to his 2006 numbers on the Jets (for sample size issues I excluded Pennington's 2009 and 2007 campaign). Here's what I found:

Brett Favre (2008/2007) (+2.94 S/100)
YPA: -1.1
Completion Percentage: -0.8
Passer Rating: -14.7
TD/INT ratio: -0.87

Brett Favre (2009/2008) (-1.03 S/100)
YPA: +1.3
Completion Percentage: +4.0
Passer Rating: +31.1
TD/INT ratio: +6.0

Chad Pennington (2008/2006) (-1.14 S/100)
YPA: +0.8
Completion Percentage: +2.9
Passer Rating: +14.8
TD/INT ratio: +1.65

Again, the results are consistent. The more often a QB gets sacked, the worse his numbers are and vice versa.

Lastly, I decided to analyze Aaron Rodgers. By following him this year, I noticed that he's getting sacked a crap ton. Due to lack of talent and injuries on his line, his sacks totals this year are far worse than they were last year. Yet Rodgers is still having a fantastic season. I think this is one example of how we underrate a QB and how it still is possible to perform with an awful line (although extremely difficult) and how we undervalue QBs who perform at an extremely high level despite their line. Here's Rodgers season this year compared to his season in '08:

Aaron Rodgers (+6.27 S/100)
YPA: +0.7
Completion Percentage: +1.2
Passer Rating: +8.8
TD/INT ratio: +1.65

Now I realize how extremely crude and unscientific my data is and how there still is a huge sample size problem. However, I have neither the time nor the knowhow to prove how sacks exactly correlate to stats such as YPA and completion percentage. I'm sure this isn't THAT hard to do so I ask all you stats, football freaks like me to help me out and find exact data for me. It may already exist and I just don't know about it, but any expansion on my data would be greatly appreciated. Also, I've just started using S/100. I don't want to say I made it up because I feel a stat like that already exists, but again, I just don't know, so in the meantime, I'm going to use it.

Thanks guys, I hope my post has been informative. To read the full posts go to:

Posted by: kaptrap19 on 25 Nov 2009

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