That's a pretty different guy. He's almost tripled his strike-out rate while turning from a groundball pitcher into a more neutral one (some of the grounders turned into flyballs, and some into line-drives - or so says Fan Graphs). Improved control is also nice, and the home run rate is probably due more to bad luck than more balls in the air (note the 4.32 xFIP).
Edit: Updated July-August stats with last night's game:
So he's more groundbally - 15 grounders to 3 flyballs will do that - but everything else stands, more or less.
Using the MLB classifications, let's take a look at his pitches. First, the usage and velocity (courtesy of Texas Leaguers).
|4S FB||Velo||2S FB||Velo||Slider||Velo||Change||Velo|
No wonder his groundball rate went down; he's traded out the two-seamer for the four-seamer. The velocity has ticked up across the board, and Bergesen sat at 91-92 with the heater his last couple starts (certainly higher than normal). Now the whiff rates:
|4S FB||2S FB||Slider||Change|
He's still not missing many bats with any of his pitches*, but the slider and change-up are both improved. Since he's going to those two pitches more often - especially the slider - it makes sense that his strike-out rate would have gone up. Trading out the sinker for the harder - and harder to hit - four-seamer adds a little bit extra there as well, and it might be making his other pitches better by relation (the change works better following a four-seamer than a two-seamer according to this research done by Josh Kalk, for example).
* Though after getting 8 swings and misses on his fastballs last night - plus couple on the slider and four on change-ups - his whiff rate on four-seamers increased to 7.5% and on two-seamers it jumped all the way to 11%. For change-ups it's almost 22% now, since the start of July.
Movement-wise, he's getting less sink on his fastballs overall (duh), but more tailing action on the four-seamer and less on the two-seamer (seems like maybe a trade-off going on there). The slider is dropping more, with movement closer to 11-5 than the 10-4 it was previously - perhaps because he's dropped his release-point when throwing it a little (he's actually throwing from a lower angle in general). As for the location, Bergesen is pitching higher in the zone - which makes sense since he's using the sinker less - and also throwing strikes more instead of nibbling off the corner. Which... makes me suspicious. Last year he threw a lot of pitches off the plate to his arm side (outside to lefties). Earlier this year was the same. The last couple months, that hasn't been quite the case. Through June, only 46.4% of the batters Bergesen faced were right-handed. Since the start of July, it's been 57%. Take a look at his career platoon splits:
That fits pretty well with his improvement from April-June to July-August. And so it appears the recent success is partially a mirage; he's been feasting on righties, and that's made his numbers look a lot better than they should. On the flip side, facing all those lefties early in the year made his numbers look worse than they should have (last season he faced about an equal number of each). Obviously he didn't go from facing 100% lefties to 100% righties though, and the change in platoon proportions might explain something like a quarter of a run difference. I was all excited to see a new and improved Brad Bergesen having success that he might be able to maintain, but that last part put a bit of a damper on it. While he is somewhat new - velocity is certainly higher and his pitch usage has changed even when adjusting* for batter handedness - how much of the improvement will last is the question. Even as he goes back to facing more lefties, if he keeps pitching like he has than he should be able to give the team close to league average innings instead of the replacement level ones from the first half of the year.
* He really is pounding the zone more against lefties too. He's been a little more willing to go inside, and is throwing fewer pitches off the plate. Before it was sinker, down and away. Sinker, down and away. Sinker, down and away. Now he's going right after them with fastballs, and is even going to the off-speed stuff more often. His approach against righties has changed some - more four-seamers and slider, though he was already predominantly using both - but not to the same degree.