Guest column by Ben Baldwin

The pair of pieces I wrote for Football Outsiders last offseason have generated a lot of discussion and follow-up questions. With the Rams' and Chiefs' offenses becoming unstoppable juggernauts in part because they use play-action at high rates, interest in what drives play-action success won't go away. Let's tackle a few questions here. I'll be using the same data that I introduced in the previous pieces, so check those out first if you haven't already.

1. We've seen that there's no clear relationship between a team's rush attempts and play-action efficiency leaguewide. But what if there's a real effect that's obscured by variation across teams' baseline passing effectiveness?

To this point, we have focused on looked at yards per play only on play-action dropbacks. But perhaps rushing increases a team's play-action benefit relative to what it otherwise would have been on other passing plays.

To test this, let's take the difference between a team's yards per dropback when using play-action and when not using play-action. If we think of non-play-action as a team's baseline passing effectiveness, then we can see whether rushing frequency or effectiveness is related to the increase in effectiveness when using play-action. Here's what the relationship looks like from 2011 to 2017:

As we saw when looking at play-action yards per play, there's no relationship here. The difference in the effectiveness of a team's passing game using play-action relative to without play-action is unrelated to the frequency or effectiveness of the team's rushing.

The most interesting part of these figures is the vertical placement of the dots. I've drawn a horizontal line at zero on each figure, and the vast majority of points lying above the line means that the vast majority of teams have more yards per play on play-action dropbacks than on non-play-action dropbacks. This isn't news -- Football Outsiders has documented play-action's efficiency for years -- but gives a visual for how rare it is for teams to fall below the zero line. And once again, there's no relationship between a team's rushing frequency or effectiveness and their likelihood of falling below the line.

Verdict: Unsupported.

2. We've learned that a team's effectiveness on play-action is not related to its rushing frequency or success. But coaches appear to believe that it does. Do teams use play-action at a higher rate when running more often?

The motivation behind this question stems from the first two weeks of the 2018 NFL season. During these two weeks, the Seattle Seahawks barely ran the ball (38 rush attempts to 81 combined pass attempts and sacks), and perhaps as a consequence, only used play-action on 12 of 81 dropbacks (15 percent). In subsequent weeks, the Seahawks would become one of the most run-heavy teams in the league. At the same time, they started using play-action frequently. Now at 31 percent, Seattle has risen to No. 3 in the league in play-action rate through Week 13. Offensive coordinator Brian Schottenheimer's comments later in the season implied that the Seahawks leaned on play-action more in later weeks because of their run game:

It helps when you're running the ball as well as we've run it the last couple of weeks. The play-action game is going to be there [...] It looks different these last two weeks than it has obviously the first two weeks when we weren't running it as well as we are now.

Oh, and if you're wondering whether play-action was still effective during those first two weeks when the Seahawks went with a pass-heavy approach, it was: Russell Wilson completed 80 percent of his passes at an absurd 18.5 yards per attempt.

Let's see whether coaches' beliefs about play-action drive how often they use it. The graphs below show the relationship between a team's rushing frequency and the percent of dropbacks that use play-action over the course of a season:

At last, we have finally found an avenue through which rushing appears to affect play-action passing: through coaches' beliefs about how often they can use play-action. (The numbers look fairly similar when looking at neutral game script situations.) While every piece of evidence we have points to those beliefs being misguided -- teams that don't run at a high rate could also use play-action frequently -- they translate into differences in play-action utilization.

Verdict: appears to be true

3. Rushing doesn't appear to set up play-action. But what about the reverse: could using play-action frequently set up a team's run game?

Frequent use of play-action could sow uncertainty in defenders' minds and lead them to be less aggressive in their run fits if they are concerned with defending the pass. For a supporting anecdote, check out Reuben Foster backpedaling here while Todd Gurley is in the midst of receiving a handoff:

.@RamsNFL offense takes all of the aggression out of defensive players. Watch #ReubenFoster be put into a deep freeze. #BaldysBreakdowns pic.twitter.com/JZxcPbynkS — Brian Baldinger (@BaldyNFL) October 23, 2018

With the Rams using play-action on 37 percent of dropbacks through Week 7 -- the most in the league by far -- perhaps Foster's indecision is no coincidence.

Let's take a look at how often teams use play-action (as a percent of dropbacks) versus how successful they are at rushing:

Here we indeed see a positive correlation, but the direction of causation is difficult to get at. It could be the case that a heavy dose of play-action forces defenses to divert resources away from defending the run. But it could also be the case that having a higher rushing success rate leads teams to use play-action more frequently due to coaches' beliefs about what makes play-action successful.

Verdict: Worth further investigation.

4. Does using play-action too frequently diminish its effectiveness?

Already we should be skeptical here given the success of the Rams this year, but let's take a look anyway.

Whether looking at play-action yards per play (left) or the difference between play-action and non-play-action (right), there's not much of a relationship. If anything, teams that use play-action more often are slightly more effective at it, which should perhaps not come as much of a surprise. (If you're wondering about the outlier in the upper right of these figures, that's the 2012 Redskins, discussed more here.

Looking at the 2018 season specifically, four of the top five teams in play-action frequency through Week 13 -- the Rams, Seahawks, Patriots, and Chiefs -- are also in the top five in play-action yards per play. The outlier is the Eagles, who use play-action at the second-highest rate in the league but are only 16th in play-action yards per play. If there is a point where play-action has diminishing returns, we don't appear to have reached it yet.

Verdict: Unsupported.

Conclusion

We have an ever-growing body of evidence that teams don't need to run often -- or run well -- to set up play-action. Play-action works for teams that run frequently, infrequently, well, or poorly. For the vast majority of teams, it just works. From 2011 to 2017, 196 of 224 team-seasons had higher yards per play on play-action dropbacks than on non-play-action dropbacks. This includes teams like the 2017 Lions (9.4 yards per play-action play, No. 30 in rushing DVOA) and 2015 Jaguars (1.7 more yards per play on play-action dropbacks despite being No. 28 in rushing DVOA and only running 31 percent of the time).

For every team observed to have a strong play-action game and strong rushing attack, I can find an example of an effective play-action team that has a weak rushing attack. For every play where a successful play-action pass followed a series of runs, I can find a play where play-action succeeded despite not recently running. There just doesn't seem to be anything there.

Finally, there's no evidence of teams using play-action a lot seeing any less benefit to play-action. Coaches treat play-action as a fragile toy that can only be brought out under certain conditions -- only after running, and only if it hasn't already been used it too much -- but it's more like the tennis racket I've had since high school: always ready, and always effective.

An economist by trade, Ben Baldwin uses large datasets to try to learn about human behavior. He can be found covering the Seahawks for The Athletic Seattle and on Twitter at @benbbaldwin.