Deflategate and handling one's balls: Turnovers, fumbles and the 2007 rule change

After the 2006 season, the NFL changed the rules to allow each team to use footballs to their liking. According the league this rule change was lobbied for by both T*m Brady and Peyton Manning in the hopes that this would keep home teams from supplying visiting teams with "bad" balls during critical points in the game.

This means that the balls used since the 2007 season should have given more advantage to all offenses.

Theoretically fewer fumbles should be occurring and fewer interceptions should be thrown IF (and this is a big if) modification of the balls to a team's liking helps prevent turnovers. This has gotten a great deal of scrutiny recently because of "Deflategate" and the article written by Warren Sharp finding that the Patriots have been amazingly able to avoid fumbles since 2010. My analysis of the data shows that the Pats are the best team since the rule change at avoiding turnovers, but not by a staggering margin (jump to the first chart below if you want to see the numbers). Let's look at some possible reasons why the Pats have been the best at NOT losing fumbles since 2007 (they have still fumbled but they have been lucky and gotten many of them back).

Possible explanations

There are five possible explanations listed in Sharp's article but for me the best explanation is either under-inflated balls (assuming they provide added ball-security) or Belicheck's stated (and practiced) policy of benching guys who fumble. If the fumble-prone players on the roster aren't carrying the ball, then your team should have fewer fumbles. Since the Patriots have been able to continue to score effectively, this means that the benching of TEs, WRs and RBs who fumble has not hurt their offense. This strategy only works if you ball-carriers are essentially interchangeable; there is little or no loss of performance when you insert the backup and bench the "starter" who just fumbled. The other side of this is the QB. Scott Kacsmar just showed that since 2007 Tom Brady has dramatically improved his ability to NOT fumble. The net result has been the Patriots' historically low fumble rate.

Comparing the Turnover Data (Plays per Turnover)

The entire league has gotten better over time at not turning the ball over, but the rule change with the footballs appears to have made it easier.  Look at the graph below comparing turnover rates 2000-2006 vs 2007-present.

Only a handful of teams have gotten worse in the last 8 seasons relative to the the first 7 of this century

The Patriots went from being an average team in terms of turnover rate (2000-6) to being the best team in the league (2007-14). Green Bay has been almost as good at avoiding turnovers over the past seven seasons. They were one of the worst teams in the league during the 00-06 time frame at turning the ball over. Green Bay shows the greatest improvement from the early time-frame to the late time-frame. It is interesting to note that 7 of the top 10 teams in terms of not turning the ball over play home games outdoors and only one of the top 5 plays indoors (IND). The average NFL team has improved by 5.2 plays per turnover in the last 8 seasons relative to first 7 of this century.

Focusing on fumbles lost (plays per fumble lost)

So if we leave interceptions out and focus solely on fumbles lost (because interception rates are largely a function of the quality of the QB) we get the chart below.

I was surprised to find that the Patriots were not the best team over the past 8 seasons at NOT losing fumbles, they are #3. Both the Colts and the Ravens have been better. Denver has been in the bottom third of the league in terms of lost fumble rate since the rule change. To get a clearer picture of how much, if any, this rule change has effected ball security we need to look at ALL fumbles.

Expanding it to all fumbles (plays per fumble)

Again I have parsed this as a rate stat (plays per fumble).

Plays per Fumble this Century

So while we see that the Pats have been the best in the league since the rule change, they are only a little bit better than the Saints and the Falcons since 2007. If we postulate that the 2007 rule change has made a difference (and the data shows that it has), then it would appear that there are four teams who are "off the line" since then: New England, New Orleans, Atlanta and Indianapolis. Have they all been doing something differently from the rest of the league since then? The results would suggest as much, but we have to be careful. Doing something differently from the rest of the league is not the same as doing something that is against the rules (although, interestingly, the Pats, Saints and Falcons have all been caught cheating recently).