Sacks are a quarterback stat. When you hear announcers talking about sacks, though, it is often in the context of the offensive line. The quality of blocking, the defense, and the passing scheme can all play a factor. But sacks are very much a quarterback stat, moreso than other stats frequently cited when talking about a quarterback.
Here, for example is an article talking about the Colts’ improvement on the offensive line, and one of the things cited is the vastly improved sack rate. It goes through each of the personnel changes on the line, and also talks about the backs and tight ends and even wide receiver Ryan Grant being graded as the #1 receiver at blocking. It doesn’t, though, credit the top reason the Colts went from a sack rate of over 10% to 3.4% this year: Andrew Luck returning in place of Jacoby Brissett. This isn’t to say that other players haven’t also made a difference, it’s just that Andrew Luck and his career 5.3% sack rate is the biggest one.
I know this is not breaking news to the small subset of the population who we might call the analytical wing of the football community. It’s an idea that has been around for at least 15 years. Back in 2009, I did a couple of studies to illustrate it, where I looked at what happened when quarterbacks changed teams, and what happened to passing stats when teams changed quarterbacks. In both cases, we were changing some elements (teammates and coaching when a QB changed teams, and changing the identity of the QB playing with mostly the same teammates and coaching in the reverse example).
Here was my summary of the results:
"Which brings us to sack rate. It is one of the most consistent things when a quarterback changes teams. It is one of the least consistent things when a team changes quarterbacks. This tells me that the quarterback plays a larger role than people think in determining a team’s sack rate. Again, I don’t know what exact percentage is attributable to the quarterback versus the line, and I certainly don’t think the line is irrelevant in determining a quarterback taking hits. I just think we measure line play by the wrong stat if we focus solely on sack rate. Sack rate does seem to have a lot to do with a quarterback’s style, decision making, and willingness (or unwillingness) to gamble with a throw before ready. A quarterback with a tendency to take fewer sacks is going to get rid of the ball; it’s his yards per attempt and completion percentage that are going to reflect whether the line did a good job. Was he throwing the ball when he wanted to, or before he wanted to?"
I’m going to add another illustration of that today, and then I’m going to move on to attempt to start answering that question that I pushed off nine years ago, about how much responsibility of a sack rate was the quarterback versus everything else.
So, in the past, I looked at quarterbacks changing teams, or teams using multiple quarterbacks in the same season. But we have this large population of quarterbacks who have long careers, rarely split seasons, and play mostly for the same franchise.
For the latest test of sack rate versus other commonly accepted QB stats, I took every QB who threw 224 or more passes at least six times since 1988, and looked at the variation in their performance in the following: completion percentage index, yards per attempt index, touchdown rate index, interception rate index, and sack rate index scores. I rated each of those QBs by their relative rank in each category, from 1 (the category where they were most consistent over their career) to 5 (the category where they were least consistent). The idea here is that the more consistent a QB is in a category, the more that the quarterback skill contributes to the measurement, while the less consistent categories have more luck and other outside factors, like different teammates and scheme, contributing.
Here are the results, listing the average ranking (where 1.0 would mean that category always ranked first) and also listing the percentage of time that category was among the two most consistent.
- Completion Percentage: 2.5 average rank (52% of time among two most consistent categories)
- Sack Rate: 2.6 average rank (53% of time among two most consistent categories)
- Yards per Attempt: 3.2 average rank (30% of time among two most consistent categories)
- Interception Rate: 3.4 average rank (33% of time among two most consistent categories)
- Touchdown Rate: 3.4 average rank (32% of time among two most consistent categories)
This matches up with everything else. Completion percentage and the percentage of time a quarterback takes a sack are the two most consistent things over a career. Completion percentage can be influenced by scheme, philosophy on types of routes, teammates and opponents, but it also has a lot of accuracy baked in. Sack rate can be influenced by those things as well but has a lot of pocket awareness and ability to read defenses pre-snap and post-snap built in.
Yards per attempt is next–and it’s probably ranked a little lower here because of some survivorship bias, as it’s the primary predictor who gets to keep playing and get to six seasons. That is to say, quarterbacks who consistently put up poor YPA numbers don’t last.
And then, you have the two things that people point to, touchdowns and interceptions. They are the most variable/least consistent measures of quarterback play.
Next week, I’m going to try to come up with the answer to just how much of the sack stats belong to the QB, and compare it to the other rate stats. I’m going to do so by looking at that same variation and the range of outcomes for individual NFL quarterbacks over time.