How Turnover Margin Affects Win Probability and Win Totals in the NFL

Every season bettors make the assumption that NFL teams that were good and bad the previous season (barring huge roster turnover) are largely going to perform similarly in the upcoming season. However, as some more well-versed bettors know there are some key indicators that can help identify which teams over- and underperformed in the win column. One of those key indicators is turnover margin.

The importance of turnovers

In a study conducted by the Harvard Sports Analysis Collective, it was found that a team that wins the turnover margin in a game wins 69.6 percent of the time. To demonstrate the relative strength of turnover influence, home teams won “just” 57.2 percent of all games in the same sample. The effect is compounding as well, as teams that won the turnover margin by two or more won 83.9 percent of the time and 90.7 percent of the time when winning the margin by three or more.

In addition to that, the study found the effect to be rather significant on a seasonal basis. Each additional positive turnover towards a team's margin is worth about 0.2 wins with an R-squared value of 0.419. For the less statistically-inclined, that means that while ignoring all other factors that impact winning and losing (point margin, opponents faced, etc.), turnover margin explained 41.9 percent of the variation in regular-season wins.

Applying this concept to the 2022 season, the top 15 teams in turnover margin were no worse than one game under .500 and seven of the top nine teams made the playoffs. Conversely just one of the bottom ten teams in turnover margin had a winning record and just two of the bottom 17 teams had such records.

Team-to-team effect

Zooming a little farther out, teams since 2016 that had a double-digit positive turnover margin saw an average decrease of 10.3 in their turnover margin in the following year. Those same teams went from averaging 11.2 wins in their turnover-friendly seasons to averaging 9.6 wins in the following season, a 1.6 decrease in wins. Only five of the 30 teams to post a +10 or higher turnover margin during this stretch did it again the following year.

Conversely, teams that had a double-digit negative turnover margin during that time saw an average increase of 14.5 (!!!) turnovers in their turnover margin in the following year. Those teams went from averaging 4.8 wins to 7.3 in the following season, a 2.5 (!!!) increase in wins. Only three of the 31 teams to post a -10 or worse turnover margin during this stretch did it again the following year.

The teams to keep an eye on this year are the Niners (+13), Cowboys (+10), Saints (-11), and Colts (-13). These teams, according to the aforementioned data, are more likely than not to have both their turnover margin and wins swing the other way.

Are turnovers predictive?

So, we know over- and underperforming in the turnover category is predictive of future performance, but are turnovers themselves predictable?

As an extension of Harvard Sports Analysis Collective's findings, they modeled the likelihood of a turnover being attributed to talent as opposed to luck, borrowing some methodology from Tom Tango - a sabermetrician.

The findings showed that about 46 percent of all turnovers could be attributed to talent (quarterbacks with low/high INT percentages, defensive linemen particularly proficient at strip-sacks, ballhawk defensive backs, etc.) and the remaining 54 percent to luck (tipped interceptions, the way the ball bounces on a fumble, etc.).

In essence, fumbles themselves are not very predictable. Given that we know that each incremental fumble towards a team's turnover margin is equal to about 0.2 wins, this creates both positive and negative performances that are extremely hard to repeat at both ends of the turnover margin spectrum. This contributes to misled optimism and pessimism towards these extreme performers when it comes to predicting the future success and failure of teams.

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