It’s possible Andrew McCutchen hasn’t been the hottest hitter in baseball, but at the very least, there haven’t been many much hotter. What makes the year notable, though, is that — as late as early May — McCutchen’s OPS was rattling around in the .500s. McCutchen didn’t go from good to red-hot. He went from bad to red-hot, and it’s worth examining the turnaround. Especially since I went to the trouble of examining his slump several weeks back. There was a time when people were legitimately worried about the Pirates’ best player. Now it’s all peaches.

It was on May 8 that I published an article titled “The Matter With Andrew McCutchen,” for JABO. Part of this article will now have to review that article, but understanding what was happening is critical for understanding what’s changed.

We’ll begin with some example swings from 2014. Here are three of them. I want you to pay attention to McCutchen’s back foot.

You see very similar behavior, which you should. Good players have consistent swings. Right around contact, McCutchen’s foot comes up, and it drives forward before slamming back into the ground. McCutchen didn’t design his swing specifically concentrating on his back foot, but what this demonstrates is good and mostly complete weight transfer. Because of that weight transfer to the front leg, McCutchen’s foot leaves the ground. You see this with Bryce Harper and a bunch of other guys. It’s not a coincidence McCutchen has hit for so much power, for a guy who doesn’t have a gigantic frame.

Here are a couple swings from early 2015. Keep looking at the back foot.

You don’t have to be a swing expert to spot the difference. I know that because I’m not a swing expert, and I can spot the difference. That back foot doesn’t really come up. Means there’s less force in the swing coming from the lower body. The lower body is supposed to generate a lot of the force. Some scouts who were watching McCutchen thought his early 2015 swing was pretty much all arms.

It would be weird for a player to just have a different swing for no reason. With McCutchen, though, a potential reason was simple enough to propose. For some months, he’s been bothered by discomfort in his left knee. Clint Hurdle said not long ago McCutchen still isn’t playing at 100%. You can see how an achy left knee might have an effect on swing mechanics. Particularly this kind of effect. Incomplete weight transfer forward could be a protective mechanism, trying to keep stress off the leg. It wouldn’t be deliberate, but it’s the kind of thing that can happen when you play through injury.

McCutchen, for a while, insisted pain wasn’t the problem. Hurdle agreed the problem was more mechanical. It seemed like there were two options. One, McCutchen was hurt — simply too hurt to consistently swing the way he wanted. In that case, it could be a problem all year long. Or two, McCutchen simply got into a bad habit earlier in the year when he tried to play through pain. Then it would just be a matter of correcting the mechanics, provided the knee could take it. In that event, McCutchen could rebound in a hurry.

Let’s look at some more recent McCutchen swings.

There’s that weight transfer. There’s that back foot coming up. Maybe it’s a little less aggressive compared to 2014, but that much is impossible to say. It certainly looks a lot more normal than the swings from early 2015. Over the past several weeks, McCutchen has managed to re-involve his lower body. It’s not an accident his numbers have soared.

McCutchen might not be 100% — and he might not get to 100% during the season — but he’s feeling well enough to have made the necessary tweak. I don’t know when his swing might’ve gone awry, but it could’ve been spring training. And then it doesn’t take long to submit the wrong things to muscle memory. McCutchen had to iron that out; he had to stop swinging as if he didn’t trust his left knee. He’s gotten there, and unless the knee pain flares up again, this should be how he remains. It appears McCutchen was telling the truth — the problem wasn’t ongoing knee pain. The problem was earlier knee pain, and the side effect on his swing.

Out of convenience, let’s split McCutchen’s season at the date I wrote that article.

Date PA wRC+ ISO BABIP GB% Hard% Through 5/7 116 78 0.110 0.229 46% 32% Since 5/8 152 185 0.256 0.381 31% 43%

I’m not sure he could be a more different player. Tons more power, now. Lots more hard-hit balls, fewer balls on the ground. From an outsider’s perspective, all it really looks like is basic regression to the mean — a great player broke out of a slump and resumed being great. In reality, there’s been a little more going on. McCutchen has regressed toward his mean, but it took some work on the very core of his offensive approach. He had to fix his swing before he could fix his statistics.

Before wrapping this up, let’s pull some numbers from Baseball Savant. It’s been suggested that one of the benefits of Statcast data could be better identifying when players are playing through something. I’m not sure how that’ll work out, but McCutchen offers some support for the theory. Through May 7, McCutchen had an average batted-ball speed of 88.1 miles per hour, ranking him at the 41st percentile. Since May 8, he’s had an average batted-ball speed of 93.2 miles per hour, ranking him at the 95th percentile. Between those two windows, he’s had the fifth-biggest increase in the league, less than one tick from first place. We’re talking about just five miles per hour, but that’s a heck of a change to your average. And presented below, McCutchen’s rolling averages of samples of 20 balls in play:

The hard contact is there. It wasn’t there before, but now it’s here — consistently. Andrew McCutchen is back on track, and the Pirates are trying to win the World Series. It’s not that there wasn’t anything to worry about. There was a problem. McCutchen solved it.