Fumbles and Luck

There’s a lot of disagreement about how much of a role luck plays in turnovers, and fumbles in particular.  I’ve addressed this in more detail before (search fumbles for the posts), but today I just want to throw out some quick data to give a better illustration of the overall points I’ve been trying to make.

First, we can mostly agree that fumble recovery % is luck-dependent.  Not all fumbles are created equal, and where they happen can effect which team recovers.  However, I think it’s fair to say that, in general, teams should recover around 50%.

Last year the Eagles recovered 35% (according to Teamrankings).  Buffalo was worst in the league at 30.6%.  Washington led the league at 67.39%.

I previously looked at the persistence of fumble recovery rate and, as expected, found no meaningful correlation.  While that’s not enough to prove recovery rates are entirely luck, it is enough to show that the Eagles are very likely to improve on that measure next year.

Fumble Differential

We’ve talked about TO Differential, but now I’ll look at pure fumble differential (gained-lost).

– The 2012 Eagles’ fumble differential was -17, or 2nd worst in the last 10 years.  Obviously, the NFL average is 0.

– There is no evidence of persistence in fumble differential.  That means, despite how bad the Eagles were with fumbles last year (-17), that has no predictive power for what that measure will be next year.

– Something to remember here is that the differential also includes fumbles forced and recovered.  The Eagles gained just 5 last year.  The NFL average is 11 over the past 10 years.  The lowest over that time was 3, not far off from the Eagles’ 5.

So let’s back away from the luck aspect for the moment (that takes a lot longer to address, particularly regarding “fumble-prone” players).  What I’m basically say is this:

– The Eagles are very likely to fumble less next year.

– The Eagles are very likely to force more fumbles next year.

– The Eagles are also likely to recover a greater % of all fumbles next year.

Regardless of where you stand on luck vs. skill, I’d be surprised if many people disagreed with any of those three statements after looking at the data.

Put those together and the Eagles are very likely to have a significantly improved fumble differential, which obviously means the team is likely to have an improved overall TO differential.

Note: Nothing is guaranteed here, we are just talking about probability.  Just because the team was unlucky last year doesn’t mean it can’t ALSO be unlucky next year.  That’s possible.

The key here is that there appears to be extremely LITTLE room for the team to get worse (because of how bad they were), hence they will likely get better.

There’s also the issue of interceptions, which I haven’t really addressed.

I’ll try to tackle interceptions sometime soon, but I wanted to be very clear about the overall ideas here.  Even if you believe fumbles are not inherently luck-dependent, the Eagles are still very likely to improve next year.

I want to make sure we’re not losing the forest for the trees here.  I’ll tackle the luck vs. skill issue in more detail later and provide further evidence for why I believe fumbles are heavily luck-dependant.

BTW, this post is the result of a very thoughtful email from someone who raised a few issues with my previous post.  As I’ve said before, I make no representations for being perfect, so critiques are both welcome and necessary.  Please email me at  eaglesrewind@gmail.com if you have any issues with posts I put up.  I’d rather have the chance to fix mistakes or explain assertions than have individual monuments to my stupidity preserved for posterity.

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3 thoughts on “Fumbles and Luck

  1. I’ll be very interested to see if teams forced interceptions is a skill or just luck. My guess is luck, because of how the schedule works out (You can even see it with players, while some always gain interceptions even the best ones like Samuel have a huge spread in how many he gets in a year). Where on offense I think its more skills based (a QB like Brady hardly ever throws ints, of course some QBs like Eli is very volatile in how many he throws)

  2. I can’t be sure at this point, but I seem to remember reading similar articles this time last year on the same subject, basically that basic mean regression would make the team better on fumbles and that the 2011 Eagles were subject to some really bad luck. if that can be confirmed, that would be enough to dampen some of that optimism.

    Obviously changing out a huge portion of your starters and your entire coaching staff will make force some kind of change, though, so there’s that bit of uncertainty?

    • Well you’ve hit on the biggest problem with analyzing this type of data. While there might be no correlation or predictive value, its hard to prove its luck because of all the roster changes (itd be possible but it would take an outrageous amount of time).

      I don’t recall reading that, but that doesn’t mean it wasn’t written. For the record, the 2011 TO Differential was -14 and the fumble differential was -4. Both are bad, but not nearly as significantly bad as the 2012 measures. Therefore, it would have been hard to point to them after 2011 as sources of big improvement.

      It’s possible to be unlucky several years in a row, it’s just extremely unlikely for the team to be as bad again next year as they were this year.

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