What happened to Buster Posey’s power?

Buster Posey hit a home run against Clayton Kershaw Monday night and it was lovely, and for one beautiful, fleeting moment, I thought that maybe this article would be dumb and unnecessary and there wouldn’t be any reason to write it. Maybe this, his first extra base hit in almost a month, would be the sign that he was breaking out of his slump and starting to hit for a little more power again, like he used to. You know, in the old days. When the Giants were winning World Series and whatnot. Boy, that was swell.

Then he didn’t get any more extra base hits over the rest of the series and, well, here we are.

Buster Posey is a career .308/.374/.475 hitter, and in the first half of last year, he was right on those averages, hitting .292/.366/.478 with 11 homers and 19 doubles in 331 plate appearances. In the second half, the average and OBP declined a bit, but the slugging cratered, leading to a line of .282/.357/.383. Posey only hit 3 homers in 283 second half PAs last year, and though he did hit 14 doubles, the lack of homers was enough to drive his slugging down.

So far this year, while his overall line looks better because of a high BABIP, Posey’s still not hitting for much power. His line is .346/.420/.449, which is a good line for a player, but if you look at difference between his secondary averages and his batting average, they’re practically identical to his second half last year. In other words, he’s basically the same hitter he was then, only luckier. In other other words, his power is still gone.

Let’s look at a heat map!

Okay, I don’t actually know what the P is in ISO/P. Does that mean per pitch? It’s already a rate stat. Why would it be ... Whatever. Let’s look at another heat map! Where I understand what everything means!

Okay, since the chart is scaled to .800 as red on the left and .305 as red on the right, it’s actually not that useful to compare, so let’s ... There really aren’t other heat maps easily available on the Internet, huh? Fine.

What you can see here (and the charts don’t agree on some of the specifics, which is fun) is that since the All-Star Break last year, when this power slump started, Posey’s gotten much worse at hitting for power on pitches inside the strike zone, and lost just about all ability to hit for power on pitches outside the strike zone. But since this is pretty universal, and it’s not like pitchers entirely stopped throwing the ball in his happy zone (SPOILER FOR LATER IN THE ARTICLE), it doesn’t explain a ton about his homer problems.

So what else is there? If you look at stats on Fangraphs, which as a baseball blogger is literally all I’m qualified to do, in the second half last year, Posey stopped pulling the ball. In the first half, he pulled the ball 41% of the time, well above his career norm, and he hit homers on about 15% of the fly balls he hit, also well above his career norm. When his pull percentage dropped by about a third to 29%, so his HR/FB percentage dropped too, to 4%.

It’s been a similar, though less extreme, story this year. Posey’s still not pulling as many balls as he usually does, and his HR/FB rate is lower than usual. But this year, the doubles have dropped off too. Some of that could be attributed to the drop in balls that he’s hit hard — his current rate of hard hit balls would be a career low, but so would his current rate of soft hit balls. Buster Posey’s been hitting a lot of balls very mediumly so far this year.

So why is he pulling the ball so much less? Well, let’s look at where he’s being pitched.

You can see that pitchers are attacking him very similarly to how they always have, but they’re focusing a bit more on throwing to that down and away part of the zone, and giving him fewer of those inside strikes that he can turn on and hit out. However, these are not high percentages of pitches, so this is a marginal effect that might explain part of what’s going on, but not most or all of it.

There is one final thing to address here, and that is platoon splits. Posey’s always had mild platoon splits when it comes to power, with a career .223 ISO against lefties and .145 ISO against righties. This year, though, while his ISO is still .184 against lefties, which is a small drop but essentially fine, against righties it’s at .025, meaning he has one extra base hit, a double, against right handed pitchers in 40 ABs. Both of his homers this year and his other double have come against lefties, and while we’re still dealing with small samples — because of his concussion the first week, Posey’s not even at 100 plate appearances yet -- the signs are very worrying, especially when you add them to his very similar performance ending last year.

So what does all this mean? First off, while it’s tempting, none of us have the medical expertise with which to diagnose incurable 30yearoldbackitis, so we should avoid making that assumption until there’s some other evidence behind it. If you’re wondering why the lack of power isn’t evidence enough, well, Posey had similarly poor power numbers before his injury in 2011, and once he came back from that, he was a great hitter again. These things can happen without any additional meaning other than “Some months you’re not as good at baseball as you are other months and that’s just how it works.”

But admittedly, the signs so far this year have not been inspiring. Posey’s platoon splits have become more extreme, he’s hitting the ball less hard than ever, and he’s pulling the ball less than he ever has. If you combine all those things, they add up to a player who’s spent several months not driving the ball like he historically has. This doesn’t have to continue, but it doesn’t have to stop either. It would probably be better for everyone, though, if it stopped.