Last week over at Fangraphs, Chris Mitchell examined the rookie debut season of Toronto Blue Jays right-hander Roberto Osuna. As you know, Osuna jumped from A-ball to the major leagues in the spring of 2015 and performed excellently in the Jays pen, saving 20 games with a 2.58 ERA, 3.02 FIP in 69.2 innings with a 75/16 K/BB. Remember, this is a guy who had an ERA of 6.55 last year in High-A. And he's just 20 years old.
What does the future hold for Osuna? Mitchell looked at historical parallels for clues. As you may expect, there are not many parallels. Writes Mitchell:
I took every reliever season since 2002 in which a pitcher 22 or younger faced at least 200 batters as a reliever. Then, I performed a weighted Mahalanobis distance analysis using the metrics used in the SIERA formula that I normalized to league average. I used SIERA’s coefficients to appropriately weigh the variables in my distance calculations. In simpler terms, I compared Osuna’s rookie season to other young pitcher’s seasons by weighing each metric according to its importance in preventing runs. For pitchers with multiple seasons in my sample, I kept only the earliest one. Due to the paucity of early-20s relievers, a mere 31 players made it through my filters.
The list turns up some names for optimists to like: Jonathan Broxton, Huston Street, Francisco Rodriguez. Chris Sale is on the list, though of course he was moved to the starting rotation after his rookie year. But the majority of the pitchers on Mitchell's list did not end up having long and successful careers. It has been known for some time that rookie relief pitchers don't follow the same age curves as other players and often fizzle quickly. Mitchell's data backs that up.
None of this means that Osuna is doomed for certain; he could turn into K-Rod, but it does show that the winds of historical precedent don't necessarily blow in his direction.
Three related points for community discussion:
***Historical parallels aside, what do you personally think will happen with Osuna?
***Should he be converted back to starting?
***If you had to promote a pitcher who spent 2015 in A-ball and make him your team's closer in 2016, who would it be?