The simplest explanation is usually the right one. We hear this saying all the time. Ironically enough, it’s derived from a more complicated principle—Occam’s Razor—but it’s easier for us all to just use that watered-down version. Here’s the thing: I’m not a fan of that type of mindset. Sure, the simplest explanation might be a part of the answer, but in all likelihood, it’s much more layered than one reason. This is especially the case when analyzing baseball.

While I try to avoid leaning on the obvious answer, even I have my pitfalls. The biggest would be when I see power numbers are down for a particular player. Immediately, I’ll go check said player’s injury history, searching for wrist, thumb, or hand issues (which are widely believed to sap a player’s power) and if I find what I’m looking for, I’ll stop digging for other reasons. And this is where I recently made a mistake.

When previewing the Boston Red Sox season on the Effectively Wild podcast with Alex Speier earlier this week, I brought up Dustin Pedroia’s loss of power. His ISO has dropped each year since 2010, but it has really cratered over the last two seasons, falling from his normal .160-ish range to .114 and .098, respectively. When looking at his injury history, I was unsurprised to see that Pedroia suffered a thumb injury in May of 2012. He missed six games, then reinjured the thumb two weeks later and tried to continue to play through the injury, but his numbers (.210/.282/.305 in 26 games) indicated taking time off to let the injury heal might be the best course of action. After a DL-stint, rest proved to have been the wise approach as it appeared that the old Pedroia was back, and he slugged .508 in the final 67 games of the season.

But health didn’t last long for Pedroia as he injured his right thumb in the first game of the 2013 season, then sprained his left thumb late in May. The Sox second baseman only missed two games that entire year—including the postseason—and despite posting a strong .372 OBP his power was way down from his career norms. After the season, Pedroia underwent surgery on his left thumb, but that was hardly the end of his headaches. Left wrist inflammation last April likely nagged him for much of the summer as he suffered through the worst offensive season since his rookie year, before ending it early with wrist surgery in September.

So there it is, a laundry list of thumb and wrist issues for Pedroia, easily explaining why his power has dropped precipitously over the last couple seasons. But, alas, it’s a bit more complicated than that. Speier indicated that Pedroia appears healthy this spring—something Pedroia has been adamant about as well—and is making the type of contact that once earned him the nickname Laser Show. But according to Speier, health wasn’t the only factor that led to Pedroia’s power outage. Speier—who credited Brian MacPherson of the Providence Journal for pointing this out (seriously Boston, stop hogging all the great baseball reporters)—said the former MVP is also suffering from pitchers taking advantage of the lower strike zone and pounding that half with more frequency.

Sure enough, after doing some digging, the story appears to pan out.

Here’s where pitchers were working Pedroia from 2007-2012:

They're mostly working away and down, but there's a decent amount of red up in the zone, right where Pedroia likes it. Pedroia’s ISO during that time was .159 and—as anyone who watches the man work knows—he was regularly hammering pitches in that sweet spot of his. Anything up in, or even above, the strike zone, Pedroia was driving with authority:

But then, pitchers started taking advantage of the fact that the lower part of the zone was being called with more frequency. The change in approach against Pedroia over the last two seasons has been rather drastic.

Pitchers are completely ignoring the upper half against Pedroia—it's straight blue up there, as cold as ice. And so was was Pedroia, with the result being an ISO of .107 over the last two seasons.

The wrist and thumb injuries have likely done their fair share of sapping Pedroia’s power over the years, as indicated by the much smaller amount of red even in the upper half of zone seen in the above ISO chart. However, it’s clear that his power is also suffering due to the large amount of the pitches he’s seeing down in the zone, keeping him from regularly elevating and driving the ball with authority.

It’s very possible Pedroia will see a jump in ISO in 2015 compared to last summer, because his wrist and thumbs do appear to finally be fully healed. However, plainly stating that 100 percent health will lead to his power returning to his peak form isn’t as safe of a bet. It’s not as simple as that, and it almost never is.

Thank you for reading

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So Pedroia got his thumb back, but not *lowers sunglasses* his thump?
Well played, sir.
A better way of stating the basic Occam's razor is that between explanations that are equally satisfying, the one that requires the fewest assumptions is preferable.
I think the color-coding made something out of nothing -- in the top graph, 2007-2012, the top 3 boxes in the strike zone add up to 12.85%; and in the third graph, 2013-2014, they add up to 12.09%. Similarly for the middle row of boxes. For the bottom row of boxes there is more of a difference, but it's still less than 3 extra balls out of 100 hitting that area.

The differences above and below the strike zone are much more significant.

Within the zone, the color difference is largely due to scale -- in the upper graph the range of numbers is from 1.67% (bluest) to 6.33% (reddest), while in the lower graph it is 2.33% (same shade of blue) to 7.11% (same shade of red). That means identical percentages on the two graphs will look bluer on the bottom one.