Conducting a study to answer if Bills should be concerned about James Cook’s fumbles

In Week 3 of the NFL season, the Buffalo Bills experienced a setback when running back James Cook suffered his second fumble of the year. This prompted an investigation into whether the Bills should be concerned about Cook's recent fumbling issues. To address this, a study was conducted using 25 years of NFL play-by-play data, spanning from the 2001 season to the most recent one.

The findings revealed that the league-wide fumble rate for running backs was approximately 1.01 fumbles per 100 touches. Moreover, the correlation between fumble rates from one year to the next was minimal, with a coefficient of only 0.197, indicating that fumble rates are largely unpredictable and random. The study then examined individual running backs' fumble rates over the course of a season, comparing their performance in Year 1 to Year 2.

The results showed that the most fumble-prone running backs significantly reduced their fumble rates in the following season, while the least fumble-prone runners experienced a substantial increase. Even the most fumble-prone group in Year 1 had a lower fumble rate than the initially least fumble-prone group in Year 2. Specifically, Cook's fumble rate of 1.25 per 100 touches in his NFL career, including the postseason, is higher than the league average.

However, his fumble rate has increased to 2.01 per 100 touches since the beginning of 2025. Although this rate places him in the top 20% of fumbling running backs, historical data suggests that such rates often regress to the mean over time. While it cannot be definitively predicted when Cook's fumbling issues will diminish, the study indicates that regression is a common occurrence among running backs with high fumble rates.