It’s not like this fact has completely escaped me, but in looking up Jeff Karstens’ numbers since coming off of the disabled list morning I was pretty surprised to see how well he’s been pitching. If you throw out his first start back (which was an 11-hit, seven-run, bad defense, disaster) he’s got a 2.80 ERA in his last seven starts. The Pirates are 5-2 in those starts and one of the losses was last Tuesday’s bullpen disaster against Arizona.
What really impresses me about these seven starts is that Karstens is still slowly evolving as a starter. Last year he found a bunch of success, but it was hard to know how to properly attribute that success because of weird flukes like his lack of multi-run home runs. He definitely improved last year; his stamina got better, his groundball rate went up, his control was better, his strikeout percentage went up even if his rate didn’t go up (translation: he struck hitters out more regularly, but his strikeout rate didn’t change because he was also giving up fewer hits via more ground balls and moving through innings quicker). It was tough to tell, at least for me, how much of the improvement was real improvement and how much was luck. Karstens proved that he was a reliable enough big league starter last year, but I felt like it was pretty impossible to ascertain how much — if any — more than that he was.
His last seven starts have been pretty markedly different. He’s struck out 37 hitters in 45 innings. That’s a rate of 7.4 K/9, compared to 5.3 last year. His strikeout percentage is still going up, too; it was 14.4% last year and over his last seven starts it’s 20.8%. His groundballs have gone back down a bit, but it’s been more than off-set by the strikeouts. You can look at the numbers at FanGraphs; he’s getting more swings at pitches out of the strike zone, and he’s getting more swings and misses. If I had to guess, I’d say it’s all stemming from his curveball. It’s not that it’s that different this year, just that that’s where the swings and misses seem to be coming (second box). It’s definitely worth looking into a little bit more in the future (if he’s doing something like setting it up better it’s a longer analysis than just overlaying break plots, so I’ll have to put some more thought into how to do this). For now, though, it’s just worth noting that Karstens is still evolving in a positive way at age 29 and that we should probably be keeping an eye on how he’s using his curveball.