The Tangible Value of NFL Sacks

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The Tangible Value of NFL Sacks

Derrik Klassen

As the NFL Draft passed and the 2017 summer rolled around, I posed a question to Setting The Edge co-founder Justis Mosqueda: “We all know sacks are supposed to kill offensive drives, but is there actually any data on that?” To my knowledge, there isn’t, so I set out to determine how often sacks actually ended offensive possessions.

All data comes via Pro Football Reference’s ‘drive finder’ feature.

To chart each of the 1,118 sacks last season, I tracked the down-and-distance, amount of yards lost, whether or not a team converted a first down following the sack, and additional data (penalties, strip sacks, etc.) that could go along with the sack or the drive. Of course, penalties and other things can distort what would have normally been a drive-killing sack, so there were a few tweaks that had to be made.

For example, if a penalty or a muffed punt occurred on a punt or a field goal try, the sack from that drive still counted as a drive-killer because the defense initially forced the offense to get rid of the ball. However, if a sack was registered on 2nd down, but there was a defensive penalty on 3rd down (a normal down) that granted the offense a first down, then the sack was not considered a drive-killer because the defense failed to take advantage of the sack while the offense was still on the field.

Now, let’s start with a broad brush.

939 out of 1,118 sacks (83.99%) last year resulted in a drive being killed. Conversely, just 179 out of 1,118 sacks (16.01%) resulted in the offense being able to bounce back and sustain their drive, even if just for one more set of downs. The difference is staggering. Defenses are almost 70% more likely to kill a drive after getting a sack than they are to surrender another set of downs. At first glance, the old adage that sacks kill drives holds true.

Of course, not every sack is the same. Giving up a sack on first down is salvageable, while surrendering a sack on third down is almost certain death. Likewise, losing ten yards on a sack is different than losing just two.

332 sacks were given up on first down last year. When giving up a sack on first down, no matter the yards lost, offenses managed to save the drive and pick up a first down 31.02% of the time. Considering the context of having given up yardage on the first play of a drive, a 31.02% drive success rate doesn’t sound too bad. However, according to Football Outsiders’ “Drive Success Rate” stat, roughly 70% of four-down series convert for a first down or a touchdown. Even on the least harmful down to give up a sack, the impact of the loss of a down and any amount of yards is dramatic enough to cut in half an offense’s likelihood of success on a given series.

Sacks on second down are even tougher to rebound from. Of the 310 second down sacks in 2016, offenses sustained drives after surrendering a sack on second down 19.35% of the time. The drop off from a first down sack to a second down sack is less drastic than I’d anticipated, though a roughly 20% success rate is still less than one-third of the normal success rate.

As expected, third down sacks are the most common type of sack and the most detrimental. There were 462 sacks on third down in 2016. Teams were able to miraculously convert on fourth down just 16 times after being sacked on third down, which comes out to 3.46% of drives. Considering must-convert situations tend to only come late in the fourth quarter, it’s no wonder that most drives ended in punts or field goals following a sack on third down.

In the same way that the down matters, the amount of yards lost plays a role in how often teams convert first downs after being sacked. As stated above, the overall conversion rate is 16.01% after any sack. Minor sacks (0-5 yards) and major sacks (6+ yards) are different obstacles for offenses to overcome.

A minor sack could be the same negative yardage as a poorly blocked run play. Losing only a few yards is more manageable than losing six-or-more yards. When offenses gave up a sack resulting in a 0-5 yard loss, they managed to still convert a first down at a rate of 23.27%. While that is markedly low compared to the average success rate, it is more than seven-percent better than the normal conversion rate after a sack. To no surprise, the conversion rate for losses of six-plus yards is much lower. Teams only salvaged their drives 12.10% of the time when being sacked for six-or-more yards.

When both factors are put together, the results are not surprising. The earlier in the series and the fewer the yards lost, the better chance the offense has to still get a first down. Below is a chart of 1st and 2nd down splits between sacks of 0-5 yards vs 6+ yards. (Did not do splits for third down because those convert at such a low rate regardless.)

No Conversion Conversion
1st Down and Lose 0-5 Yards 69/118 (58.47%) 49/118 (41.53%)
1st Down and Lose 6+ Yards 160/214 (74.77%) 54/214 (25.23%)
2nd Down and Lose 0-5 Yards 92/125 (73.60%) 33/125 (26.40%)
2nd Down and Lose 6+ Yards 159/185 (85.95%) 26/185 (14.05%)

It is common sense that the later in a series and the more yards lost, the tougher it would be to rebound from a sack, but it’s reassuring to see that the numbers back up that claim.

In all: getting sacked is bad. Sacks, even the least harmful of them, shrink the chances of an offense earning themselves a fresh set of downs. Like any other statistic, though, some teams are more successful than others. As a follow-up to this piece, I will dive into which teams, if any, stand above the rest in terms of converting first downs after being sacked.