Third Down and Air Yards
Guest column by Nate Weller, Sports Info Solutions
There may not be another play that can get a fan yelling at his TV more quickly than a draw or screen on third down. Broadcasters generally concede that it was the right thing to do, and it is explained away as the "smart" or "conservative" play, and it is left at that. And while "conservative" is probably a fair characterization, "smart" may not be. The numbers suggest that coaches are overly risk-averse on third-and-long and would benefit from being more aggressive in these situations.
The Impact of Air Yards on Third-and-Long
To start breaking it down, throw depth was taken as a percentage of yards to gain. The underlying assumption is that a 10-yard throw on third-and-15 is much different than a 10-yard throw on third-and-10. From there, we can look at the conversion and turnover rates based on how aggressive a team was attacking the sticks on third down. The sample includes all plays of third-and-10 or longer from 2015 to 2018.
The fact that a first down is more likely when the ball is thrown to the sticks as opposed to 10 yards short is not exactly a revelation, but what may be surprising is how non-linear the relationship is. The likelihood of a third-down conversion only moves from about 10% to a little over 25% on throws between zero and 90% of the yards to gain, but it doubles if the throw is at or just beyond the sticks.
More importantly, the likelihood of a turnover remains largely constant with increased throw depth. Outside of throws at or behind line of scrimmage, there is no discernible increase in turnover rate like one might expect. On throws to the sticks, the turnover rate is only 3%, compared to the 1% on throws at or behind the LOS. (This includes fumbles and not just interceptions.)
Despite all of this, teams are still reluctant to air it out on third-and-long. From 2015 to 2018, the ball only traveled to at least the yard to gain on 36% of third-and-long throws. Those plays were converted into first downs 49% of the time, compared to only 13% of the time when the ball was thrown short, approximately four times as often.
This is a simplistic approach and there are plenty of biases that are potentially at play here. There is no sure-fire way to know what the intended route was on a given play, and all analysis is based on which player is ultimately targeted. Just because the team ended up targeting the curl does not mean that the quarterback's first read wasn't down the field. Similarly, all throws at or behind the line of scrimmage are not designed screens, and can include checkdowns. Still, on the surface, teams seem to be missing out on opportunities.
Breaking it Down by Route
Looking at target share and effectiveness by route helps provide some clarity. Chip-flats, check & releases, and flats -- the three routes most often associated with a checkdown -- are each among the least targeted routes in third-and-long situations, indicating on some level that hot reads and checkdowns aren't substantially skewing the data.
On the other end of the spectrum, curls and screens are the most targeted routes despite conversion rates of only 26.3% and 13.0%. Posts, corners, and digs -- the three routes with the highest conversion rates -- as a group were not targeted as often as curls, and only narrowly outpaced screens. Again, this is not a perfect reflection of how often teams tried to target those routes, but given the disparity in target share, there appears to be some indication that teams are being far too conservative in third-and-long situations.
The gap in turnover rate when broken down by route is more significant. There is no denying that a turnover rate of 7.1% on a post is a deterrent, especially compared to the 2.2% turnover rate when targeting a curl; overall, posts, corners, and digs make up three of the four most dangerous routes by turnover rate. Given their conversion rates, it seems like a risk teams could be taking more often.
Other Considerations on Third Down
Defensive pass interference (DPI) is another part of the equation. There is a strong relationship between the depth of a throw and the likelihood of drawing DPI. We have already done research on just how impactful pass interference calls can be as a whole, and not surprisingly, it's no different in third-and-long situations. On throws between 15 and 20 yards, a DPI call is almost as likely as a turnover, adding another important factor to consider.
The relationship continues the more teams stretch the field. Throws beyond 30 or 40 yards, while at a greater risk for turnovers, also maximize the likelihood of drawing a penalty. This begs the question, what really is the difference between a 40-yard interception on third down and a 40-yard punt on fourth down? Teams generally play it conservative on third down only to set up a punt on fourth, all in the name of field position. Sure, it may not show up in the box score, but it takes your offense off the field all the same. The small field position advantage you might gain by setting up for a punt should not outweigh a chance to keep a drive going.
To look at this another way, the worst-case scenario on a 40-yard throw on third-and-long is an interception, which has an average Expected Points Added (EPA) value of -1.1. A short pass on third down (less than 5 yards) and a punt on fourth down has a combined EPA of -0.9, only a marginal improvement on the interception. And this is without accounting for the potential that the 40-yard arm-punt could be successful.
Taking all of this on the aggregate, it's clear that teams are generally risk-averse, and tend to avoid situations they feel increase the likelihood of a turnover. It is not always prudent to be overly aggressive on third down. Field position, time remaining, and the score all need to be considered when it comes to play calling, but there is a pile of evidence that suggests that coaches are being far too conservative when it comes to third-and-long as it stands.