What happened to Denard Span's power?

Over the offseason, the Giants declined Nori Aoki's option and instead ended up signing Denard Span. And while Aoki's been awful this year, and the only reason I'm bringing him up is so you don't feel too bad about Span, Span has himself been a low-key not very good player. Giants fans everywhere have noticed that his defense hasn't been much better than average, and his hitting has been a disappointment.. Specifically, hitting-wise, he has shown absolutely no power after a career of thoroughly adequate power. What gives?

The first thing to note is that while this would be Span's worst slugging percentage in a season in his career, this isn't actually the least amount of power he's ever had. His ISO – slugging percentage minus batting average – was slightly lower back when he was with the Twins in 2010, and it was almost as low in 2011. What all three of these years have in common is that they're the only years when he's had a BABIP under .300. What two of these years have in common – not 2010, that damn slacker – is Span's unusually high percentage of softly hit balls, 27% in 2011 and 25.6% this year. Those are the only years where that stat is above 21.1%, so that's probably a big part of it too.

While a low batting average is not a great thing for a hitter with Span's skillset – high contact, high speed, low-medium power – the fact that he has easily the lowest BABIP of his career (even with a high soft contact rate) means we can probably expect the average to be a little better going forward. His power, however, enjoys no such regression optimism. So let's look at what's different. Heat maps time! (Career ISOs on the left, 2016 on the right)

You can see here that there are different colors in different areas. Colors are pretty! I like colors.

Also, the colors have meanings. At first glance, it seems like his power inside the strike zone is the problem. Look at how blue it is! The one on the left is so purple and the one on the right is blue inside the zone. That's bad. But if you look at where his power actually comes from, the strike zone isn't really where he drives the ball. It's that little square of the four boxes in the lower right where he's traditionally found all of his power (okay, half of those are in the strike zone, you're very smart, we're all impressed with you), and in 2016, he doesn't have one extra base hit on those pitches.

So then the question becomes, why is that? Have pitchers learned to avoid those areas? They've always gone away on Span, but have they learned to go even awayer, just relentlessly pounding the outside until the outside's all, "Guys, stop it. This really hurts. I'm going home"?

Nope! Just the opposite, really. Pitchers are throwing more pitches in his happy zone. So is he not swinging? He has to be not swinging at them, right? Please tell me he's not swinging, so that I can at least have that one bit of baseball analysis to be right about.

PHEW. Anything at all that could reasonably be called "down and in," which is where his power lies, he's been swinging less at. He's swinging more at higher pitches in the zone, which have never been what he hits well. Maybe Hensley Meulens's hitting philosophy doesn't work for Span, or maybe he's mechanically off and not seeing the low and in pitches, or maybe it's a small sample size fluke. But right now, he's swinging differently than he has in his career in a way that you'd expect to lead to poor results. So far, he's finding those poor results.