Turnovers are one of the most important statistics in the NFL. They're also one of the most unpredictable. Every season, we see teams that are registering a lot of turnovers suddenly stop getting takeaways altogether in the middle of the campaign. Or teams without many turnovers will abruptly start turning the ball over. Future turnover totals are a lot harder to predict than other stats such as yardage or completion percentage.
One big reason that turnover numbers are inconsistent has to do with fumbles. Essentially, recovery of a fumble has no predictive value. Teams that recover a high percentage of fumbles in one season will sometimes recover very few fumbles the next, even if there were more fumbles in their games. The reverse is also true.
Interceptions are almost as unpredictable as fumble recoveries. Over the past five years, the correlation coefficient (explained here) for offensive interceptions from the first half of the season to the second half is just 0.17. The correlation on defense is even worse, just 0.08. The defenses with the most first-half interceptions over the past five years averaged 12.9 interceptions in the first nine weeks of the season, then just 6.6 interceptions in the last eight. The defenses with the fewest first-half interceptions went from 2.5 picks in the first nine weeks to an average of 5.9 in the last eight.
We know that we can "predict" fumble recoveries by looking at raw fumble totals. Roughly half of all fumbles end up recovered by each team, although the rates are different for different types of fumbles (including sacks, aborted snaps, rushes, pass completions). Is there a stat that helps predict interceptions in the same way that total fumbles predict fumble recoveries?
It turns out there is: passes defensed.
Inspired by previous work from college football analyst Bill Connelly, I looked at passes defensed totals and interceptions from the past five years. As a general rule, NFL teams will turn 19.3% of passes defensed into interceptions. Interception totals vary from team to team, but over the long term, teams will generally regress back toward this ratio of passes defensed to interceptions.
We can do an even better job of predicting interceptions by combining passes defensed with schedule strength. This is especially true when it comes to projecting defensive interceptions using offensive schedule strength, because the offensive rates of interceptions and passes defensed are about twice as stable as the defensive rates.
We put together passes defensed totals with schedule strength (based on average DVOA of opponent) to do projections of how many interceptions we can expect from each offense and defense the rest of the way this season. In our lists below, we're going to focus on playoff contenders. However, be aware that the offensive numbers are based on team totals, not individual totals. That's an important consideration when 51 different quarterbacks have started games this season and some teams have seen a big difference between the starter and his backup.
With that caveat, here are the five quarterbacks on playoff contenders projected to throw the most -- and the least -- interceptions over the final seven weeks of the season:
Offensive interception predictions
Jared Goff, Los Angeles Rams: 6.9
Goff has nine interceptions so far, tied for fourth, and 50 passes defensed, which ranks sixth. Brissett and Jackson are on the list because Indianapolis and Baltimore will face more difficult offensive schedules the rest of the year. Wentz has just four picks, but 40 passes defensed, a 10% ratio.
Foles comes with a bit of an asterisk, because we're using team numbers here. Foles has only eight pass attempts this season, so this projection is really what we would project for Gardner Minshew II if he remained Jacksonville's starter. But Minshew is a good example of a player who has had excellent luck with passes defensed not turning into interceptions. Minshew has only four interceptions, but he has 44 passes defensed, which ranks eighth in the league. Normally, that number of passes defensed would result in twice as many interceptions. So we would definitely expect more interceptions from Minshew if he continued as the starter.
The player who is the opposite of Minshew is Sam Darnold of the Jets. Darnold has thrown nine picks with 26 passes defensed, so defenses have turned 35% of his passes defensed into interceptions. That's nearly twice the NFL average of 19.3%. Combine that with an easier schedule in the second half of the season, and our system expects only 4.9 interceptions from Darnold the rest of the way.
Here are the quarterbacks on playoff contenders projected to throw the fewest interceptions in the last seven weeks of the season:
These quarterbacks are all from teams that have only six games remaining, which is part of the reason why they have the fewest projected interceptions from Week 11 on. But that's not the only reason; except for Tannehill, these quarterbacks are also at the bottom in terms of projected interceptions per game.
Cousins has the fewest passes defensed (18) of any quarterback who has started all of their team's games. Wilson, Rodgers and Mahomes all have seen defenses turn less than 10% of passes defensed into interceptions, but they also have so few passes defensed that our projections of their future interceptions are low.
Defensive interception predictions
The differences between the past and future are even stronger on the defensive side of the ball, partly because extreme schedules have led to some dramatic early interception totals. The New England Patriots stand out the most, with 19 interceptions so far. That's come off 52 passes defensed, second in the NFL, so the Patriots have turned 36.5% of passes defensed into interceptions. Compare this to the team with the most passes defensed: Minnesota, with 55. The Vikings have only nine interceptions so far this year, for a below-average rate of 16%.
Combine New England's unsustainable ratio of interceptions to passes defensed with the fact that their schedule gets much harder over the next few games, and we project them with only 5.7 interceptions in the final seven games. That would take them from a substantial league lead in Weeks 1-10 to roughly league average in Weeks 11-17.
Here are the playoff contenders with the most projected interceptions on defense from Week 11 on. The leaders, Pittsburgh and Oakland, are both beneficiaries of schedules that get much easier than they were in the first half of the season.
Pittsburgh Steelers: 7.8
Oakland Raiders: 6.7
Houston Texans: 6.7
Baltimore Ravens: 6.4
Carolina Panthers: 6.1
And here are the playoff contenders with the fewest projected interceptions on defense from Week 11 on:
Seattle Seahawks: 4.2
Indianapolis Colts: 4.2
Kansas City Chiefs: 4.3
Los Angeles Rams: 4.3
Tennessee Titans: 4.5