When Aaron Slegers pitched for the Twins on Aug. 17, starting the second game of a doubleheader against Cleveland, he became the 33rd pitcher this season — and fourth Twin — to make his MLB debut as a starting pitcher this season.
Slegers delivered one of the most important pitching performances of the season that day, giving the Twins 6⅓ innings of two-run ball while delivering innings and a victory Minnesota desperately needed.
At the time, I was curious how common — or uncommon — it was for a pitcher to excel in his MLB debut. With help from Aaron Gleeman from Baseball Prospectus, I gathered the data on all 33 pitchers to debut this season by that point and found that, well, it has not been uncommon for first-time starters to do pretty well in 2017.
Counting Slegers, the 33 pitchers to debut as starters delivered, on average, starts that went five innings with 2.23 earned runs allowed — for a 4.22 ERA. The ERA for all starting pitchers this season is 4.51, so first-timers actually fared better than the average starter this year.
That information was gathered a few weeks ago … and then Slegers didn't make a second start for a long time … and then I went on vacation.
But now I'm back, and so is Slegers — who made another very important Wednesday start for a Twins team once again starting to slide. This one, of course, didn't go nearly as well. He made a couple of mistakes — the big one a three-run homer to Lucas Duda after a pair of two-out walks — and ended up going just four innings while allowing five earned runs.
And, as it turns out, his struggles weren't all that uncommon, either. I looked up the data on the second start of every other starting pitcher who debuted this season before Slegers. Four of them haven't had a second start, but of the 28 others who did, their average second start produced an ERA of 5.33 — more than a full run higher than their debuts, and well above the league average.
Maybe it's too small a sample to be relevant, but maybe other factors are at play.
