Monday, October 14, 2013

QB's Don't Have (Passing) Rhythm

While I have generally been able to maintain a semi-weekly update schedule, the next few months are going to be quite busy (that thesis isn't going to write itself). I will try to keep updating regularly, but I'm not making any promises. Feel free to check the blog regularly to see if there are updates, but if you'd rather use a more efficient method to see when I update put your email address into the box on the right (under 'Get Email Updates') and you'll automagically get an email each time I make a new post. If you're more into twitter, following me @PhDfootball will also let you know when I post (and has the added bonus of giving you direct access to all of my delightfully informative thoughts and comments). Regular updates will hopefully resume after the new year, when the title of this blog will be even more accurate!
'Rhythm' is an often-used buzzword in football circles, especially pertaining to a quarterback who is known for being inconsistent. To take a quantitative look at this concept I break down each pass as a function of the one thrown before it, looking for evidence that completing a pass can jump-start a passer into completing more. While this analysis is admittedly superficial, it's a good starting point to tackling this subject. Ultimately, there is no evidence that one pass completion begets another, an argument against the idea that QBs can get into a rhythm.

Last season the Jets tried to run an offense involving two quarterbacks, with Mark Sanchez running the regular offense and Tim Tebow coming in to run wildcat-style plays. This was an unarguable failure.

A common reason given by announcers and sportswriters for this unconventional scheme's lack of success was that it never allowed one quarterback to "get into rhythm." That certainly seemed true enough; several times Sanchez would complete a couple of nice passes, then Tebow would come in and run for a few yards, then the drive would stall out once Sanchez came back in.

This is, of course, the same reason given for the failure of Tom Landry's plan to let Craig Morton and Roger Staubach alternate snaps for an entire game (a loss) during the 1971 season.

As usual, there's never any attempt by the announcers to explain what 'rhythm' is or how to tell if a quarterback is in it; this wishy-washy term is generally used as a catch-all to explain why a signal-caller is (or isn't) playing well.

But maybe there is some truth to the idea. There is plenty of anecdotal (and some scientific!) evidence for players getting into 'the zone' during a game, which certainly sounds similar to the concept of 'rhythm'. And football commentators have been using the term for as long as I can remember without any pushback or criticism.

Let's take a look at the concept of QB rhythm (I'll drop the pretentious quoting from this point onward), first attempting to define it in a quantitative manner and then looking at data to determine its validity.

For this experiment I need play-by-play data, which (as usual) comes from Armchair Analysis. Next we need to quantify what statistics could be employed to quantify how much a QB is in rhythm. What would be an observable of a quarterback in rhythm?

The obvious choice is completions. Generally a QB who is in rhythm should be completing several passes in a row, while you would expect a passer who is out of rhythm to be very scattershot. It's difficult to look at completion streaks, as drives can be of variable lengths and we could accidentally bias ourselves towards looking only at very good quarterbacks, who are more likely to have long completion streaks in the first place.

Therefore we'll look at the effect a completion has on just the next pass. While not perfect, this will at least minimize the risk of bias. Additionally, to avoid including situations where one team is being blown out and throwing every play, we'll only include data from the first three quarters of games.

First of all, over the entire sample the completion percentage is a healthy but unspectacular 56.8%. If a quarterback can get into rhythm by completing passes, we'd expect the overall completion percentage on passes attempted after a completed pass to be higher than this overall figure.

Interestingly, it turns out that the opposite is true. If you only look at plays directly after a pass, NFL QBs have a completion percentage of 56.2%. If you loosen your restrictions and check the completion rate specifically for the next pass (even if there may have been several runs in between),  the completion percentage is 56.3%.

Now, it might be that our data are somewhat biased to lower completion percentages because we have to throw out the first completion of each drive. Therefore it might be that we should expect a slightly lower completion percentage than the total 56.8% figure.

To check this possibility I did 1000 random resamplings of the data, keeping the drive data constant but shuffling the type of play (and the result). For both scenarios this test produced completion percentages 56.8+/-0.2%, exactly the same as the overall completion percentage. So if anything, completing their previous pass seems to make quarterbacks more likely to misfire on their next.

Discussion and Conclusions
So what gives? While I'll be the first to admit that this analysis is by no means perfect, it seems pretty clear that this line of inquiry doesn't show any evidence for getting into rhythms. At the very least we can now say that just because a QB has completed a couple passes in a row he's not about to keep up the trend.

One important caveat, especially for the Tebow-Sanchez and Morton-Staubach situations, is that this analysis covers drives where, the vast majority of the time, the QB stayed on the field for every play. Even for wildcat plays the quarterback usually lines up at wide receiver rather than going to the bench - in this way the surprise of the playcall is preserved until the offense breaks their huddle.

With the data currently at my disposal, I can't distinguish between plays where the QB is on the field and those where he is not. Even with that information, there are so few instances where the QB does leave the field during a drive that finding any signal amongst the noise would likely be impossible.

Despite these (very reasonable) concerns, the case against QB rhythm seems fairly strong. While I could believe that quarterbacks get into zones over the course of a season, it doesn't appear to happen on a drive-by-drive basis.

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