Mean Reversion and the 2012-2013 Eagles Improvement

Jeffrey G. Pittenger-USA TODAY S

Checking in on Fumble Recovery Rate, Fumbles Lost, and Net Field position

Preseason, I did a number of posts that focused on the reasons why the Eagles finished with such a poor record last year.  The general thesis was that the team was bad, but it was also very unlucky.  Therefore, we could expect a better record this year purely as a result of reverting to the mean in several meaningful statistics.  Today, let’s take a look at a couple of them and see how they look.

First, here’s the 2012 performance dashboard I put together.

Screen-shot-2013-08-15-at-11-35-24-am_medium

Remember that I scaled everything by historical standard deviation (last 10 years of data) so that it could all be viewed in one chart.  For our purposes today, the most important terms above are Fumble Recovery %, Fumbles Lost, and Net Field Position.

Note that, for now at least, I’m going to avoid the whole luck-vs.-skill angle.  I’ve explored that before and I’m sure I’ll revisit it again.  Regardless of which side you believe in, the fact is that regardless of the role of luck, those statistics show NO PERSISTENCE from year to year.  Note also that the three stats I’m highlighting are obviously interrelated, so it’s no surprise that terrible performance in one is correlated with terrible performance in the others.

Fumble Recovery %

In general, teams should expect to recover around 50% of all fumbles.  There’s been some additional research done about varying rates for different TYPES of fumbles (Downfield WR vs QB for example), but after including all types, the overall rates converge to 50%.

Last year, the Eagles recovered just 35.09% (Teamrankings.com), which is 1.99 standard deviations below the mean.  That’s really bad, and extremely unlikely to happen again.  So how is the team doing this year?

46.34%

Not great, but a much more reasonable rate of recovery.

Fumbles Lost

Relatedly, the Eagles problem last year wasn’t just the rate of recovery, it was an overwhelming number of fumbles.  Combined, that meant the 2012 Eagles lost a historically large number of fumbles to the other team.  Looking at the chart above, we see that the team lost 22 fumbles last year, which is nearly 3 standard deviations from the mean. Like I said, historic, and a big reason why last year’s team struggled so much.

So how do things look now?

Well so far, the team has lost just 8 fumbles, or .615 per game, meaning it’s on pace for just under 10 fumbles lost, less than half of last year’s measure.

Net Field Position

Finally, for today at least, there’s Net Field Position.  As a result of both special teams and the historic turnover rates, the 2012 Eagles had TERRIBLE net starting field position.  Looking at the chart above, we see the team’s average drive started 6.67 yards behind the other team’s average starting position.  That’s a very big difference, and it’s more than 2 standard deviations from the mean.  The offense last year was actually middle-of-the-pack by yards-per-drive.  The problem was that they had farther to go than everyone else.

This year?  +1.4 yards, good enough for 11th overall (Football Outsiders).

Having trouble conceptualizing the significance of the shift?  Well consider this:

This year, the team is averaging 33.06 yards per drive.  It’s scoring 25.7 points per game.

Last year, the team averaged 31.51 yards per drive.  It scored just 17.5 points per game.

Put differently, this year’s team is gaining an average of just 1.5 yards per drive more than last year’s team did.

The real difference?  Mostly turnovers and field position, both of which we’re primed for mean reversion.

Lastly, the really good news

Did you notice anything else about the stats I just discussed?  Let’s look at them again:

Fumble Recovery %: 46.34%

Fumbles Lost:  On pace for 10

Net Field Position:  +1.4 yards (11th overall)

Now?  While last year’s numbers were EXTREMELY bad, and thus carried a very high probability for improvement, this year’s numbers are squarely in the middle of the expected range.  That means, while last year’s team was both bad AND unlucky, this year’s team is just good, no luck caveat needed, at least as it pertains to these stats.

That means what we’re seeing isn’t likely to be a fluke.  Once the season is finished I’ll look at a larger number of statistics and see where we can expect improvement or decline, but for now, it looks like the team is just good.

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