I also think it is the hard throwers. I wonder if the flies to grounders ratios have changed, too. If there are more fly balls being hit relative to grounders, and there are more fly ball pitchers throwing hard, you'll get the Scherzer Effect of dominant K totals with more home runs.
That's pretty easy to test. The data set is pretty granular, so you can see (1) if the HR rate on pitches at given speeds has changed (e.g., HR rate on 95 MPH fastballs), (2) if pitch mix is affecting it (are pitchers throwing more fastballs because they throw harder), and (3), related to (2), is there a "sweet spot" for home run throwing (I would assume that, at least for fastballs, HR rates follow a predictable distribution - very hard (97 and up) don't get hit out much, but neither do very slow (under 88 or so) because guys who throw that slowly don't stick around much unless they can keep their fastball down/on the ground) and a corresponding increase in pitches in that range driving the rise? Anyone with the full data set and a software tool could run those pretty easily.
It's more likely PEDs or a change to the ball than a statistical aberration: while it's only 1 year, that's a big sample size (almost 2700 games already). A rise that big over that size of a sample suggests something's different across the entire sample. It could be changing hitter approaches - it seems every team has 3 Mark Reynolds hitters now, it could be harder throwers, it could be PEDs, it could be a combination of all those.
