What Will Michael Brantley’s Regression Look Like

When a 27-year-old doubles his previous best in homers, seasoned stats lovers everywhere give him the virtual pat on the head. That’s nice, thanks for 2014, but we’re not moving your needle too much in 2015. You won’t be projected to be top ten in the outfield despite coming in second in the end-of year rankings this past season.

But look over Michael Brantley’s particular history — the slowly growing homer totals, and the athleticism he always brought to the table — and it’s tempting to fall in love. What might his regression actually look like, and if it’s a little better than his projections, could he make a sharp pickup in a league full of sharps, all busy patting him on the head?

You could call Brantley’s growth organic and steady. His three full seasons went 6/10/20 in homer totals, and all three seasons feature basically the same ground-ball-per-fly-ball mix — there was no sudden change in approach at first glance. year, He still has a tiny swinging strike rate (3.6% last year, 3.4% career), and even in a season that saw his power surge, he cut down his strikeout rate to a career-best (8.3% last year, 11% career). Even his batted ball stats didn’t change much. He hit his fly balls and homers an average of 280 feet in 2014, and those same balls went 276 feet in 2013.

So where did the extra power come from?

There is a clue in the fly ball batted ball angle. It looks like he went from pushing fly balls to pulling them. Let’s see if the charts agree. And, yup, he started pulling his fly balls more. Look at his angle first. Left field is positive, so he moved from pushing to pulling according to fly ball angle.

And then the spray charts. See the purple blot along the left field line in 2013 and then how those hits seem to have spread to right field in 2014:

So let’s say we’ve identified the source of Brantley’s power surge. How likely is he to continue pulling balls with success next year? What we’re asking is, what is the year-to-year correlation on pull percentage, considering he changed his pull percentage profile there?

I ran the last five years, and the average correlation was .678, which is better than batting average but not quite as stable as ISO. Another way of saying this is that this year’s pull percentage explains about 46% of the variance in next year’s pull percentage.

So it’s basically a fifty-fifty bet that Brantley continues to pull the ball as he has. Considering he’s going to be 28 next year and stolen bases age poorly, and there’s some evidence that peak age is moving earlier in the ‘post-PED’ era, it’s kind of hard to bet on the meaty side of that 50-50 coin.

The good news is that the baseline provided by Brantley before this power outburst — basically a .285/10/15 player — has become more valuable as batting average has declined around him. He’s now spent three years with an above-average stick and should continue to do so. To invest in him heavily, though, you’ll want closer to 20 homers from Michael Brantley. How do you like that coin?