Originally, this was going to be a little post about Jonathan Schoop. I wasn’t super jazzed to write about Jonathan Schoop, and you weren’t super jazzed to read about Jonathan Schoop, but, in case you weren’t already aware, Schoop is swinging a lot less than he used to. One of the very most aggressive hitters around has dropped his swing rate by right around 10 percentage points, and that’s big. That’s a significant change, for a player who had been in need of more polish. It seems like a step forward. It’s interesting.

But, at least as this post goes, the hell with Schoop, because I need to point you toward Mike Moustakas. Has it been a while since you checked in on him? I guess that depends on whether you’re a Royals fan. But let me summarize where Moustakas has been real quick. You remember he used to be a top prospect. Then he was a disappointing major-leaguer. Then the big story became that his approach matured, and he learned to take balls to the opposite field. Moustakas stopped trying to pull everything, and, at last, he found success. The game was coming together for him, and he had a strong start to 2016. Then he got hurt. Badly hurt — hurt enough to miss the rest of the year. For everyone involved, it was a tremendous disappointment.

Moustakas is back on the field. He’s played almost every game, and he’s already set a new career high for home runs. That opposite-field focus is gone; Moustakas has been killing the ball to right. In that sense, he’s reverted, although now it’s working. But that’s not what I want to draw your attention to. Before having surgery, Moustakas was more patient than ever. On the other side of surgery, he’s been more aggressive than ever. He’s jumped from one end of the spectrum to the other, as you can see in the following plot:

More swings in the zone. More swings out of the zone! More swings in and out of the zone. Moustakas has been trying to hit everything he can, and his numbers are fine, if not massively improved. To try to put this in some context, I consulted the extent of our historical plate-discipline data, which goes back to 2002. I looked at every player with at least 100 plate appearances in consecutive seasons, which gave me a sample of 5,205 individual player season-pairs. Here is a plot of their swing rates. Moustakas is highlighted in yellow.

Compared to last year, Moustakas’ swing rate is up 15 percentage points, which is the largest increase in the sample. Looking at absolute values, it’s also just the largest change in the sample, up or down. This season isn’t over yet, so, there’s that, but for now, in the past decade and a half, we haven’t seen a player so suddenly change like this. Moustakas went under the knife as a more disciplined bat. He’s come away as a hacker, and he’s really gotten no better or worse. He’s the same, but different, and to this point in 2017, Moustakas has yet to take a single called third strike.

Usually people want more from something like this. They want the author to determine whether a change is good or bad. I can’t do that. All I know is there’s been a change. It’s worked about as well as the previous changes. Mike Moustakas has already had one weird big-league career.