I watched a conversation the other day between Chris Trapasso and Sigmund Bloom regarding fumbles (go follow them if you don’t already). Chris believes most fumbles are a result of the offensive player carelessly carrying the ball and the defender hitting the player in the right spot. Basically, they got lucky to hit the offensive player in a vulnerable spot. Sigmund’s stance was that teams practice stripping the ball and forcing fumbles for a reason.
Here’s the exchange between the two:
So are forced fumbles random or is there skill involved. There are two ways to look at it. First, it needs to be determined whether certain players consistently outperform league averages in forced fumbles as a percentage of total tackles. Second, each forced fumble should be analyzed to determine whether the fumble was caused by the defender hitting the player in just the right spot when going for a routine tackle, a well timed strip, or careless ball carrying. I’ll delve into the first way in this post.
In order to determine league averages for forced fumbles, I calculated each defensive player’s forced fumbles as a percentage of total tackles (solo plus assists) from the past ten seasons. I found that the average for those ten seasons was 1.57 forced fumbles per tackle. A rare occurrence no doubt.
Based on that 1.57% forced fumble rate, we can determine whether certain players are better than the average. We can test an alternate hypothesis saying a player (Simeon Rice in this example) has a greater forced fumble rate than the league average. Rice forced 28 fumbles over the course of 475 total tackles, a 5.89% forced fumble rate. The hypothesis test finds that Rice’s forced fumble rate is significantly greater than the league average, and not a result of chance or luck. Rice was better at forcing fumbles than the average NFL player.
But forced fumbles are more common for defensive ends because they cause fumbles during sacks. Quarterbacks hold the ball in a less secure position than players running with the ball, so they’re more susceptible to losing the ball. Beyond defensive ends, the averages among the remaining positions is pretty similar. The breakdown for currently active players over the past ten years is in the table below.
So we would need to compare Rice’s forced fumble rate to the average defensive end rate to see if he was truly better than the average defensive end at causing fumbles. The upper critical value for defensive ends (95% confidence) is 5.40%. Because Rice’s 5.89% is greater, we can accept the alternative hypothesis saying Simeon Rice had a higher forced fumble rate than the NFL average. He showed a higher ability to force fumbles and we can therefore say he was skilled in forcing fumbles.
What about players that don’t get as many chances at quarterbacks? Continuing with the currently active players over the past ten seasons, a total of 97 players have forced fumble rates significantly higher than their positional averages. Some of those players may have benefited from forcing a fumble in his only twenty tackles of his career, but players like Rice indicate that forcing fumbles can be a skill.
In order to scrub the data set of the players with too few tackles to know whether they are actually better than average at forcing fumbles, I increased the minimum number of tackles to 100. Out of this group, only forty players (12.5%) had forced fumble rates significantly above their positional average. Here’s the top fifteen, including their total tackles:
I believe that because certain players can repeatedly outperform their positional averages there is a skill to forcing fumbles. The skill yields a small rate of results (usually around two percent of all tackles), which means there is some luck in terms of a player being in the right place at the right time, but the player has to be able to act on that opportunity. Like interceptions, a defender can be skillful and benefit from good luck. The fifteen players listed above have made careers out of taking the ball away from opponents.