At 33 years old, Seung Hwan Oh is not your typical rookie. Since 1960, twenty-one players had their rookie season at an older age, which to be honest, is quite a bit more than I expected. The large majority of them, like Oh, had long, established careers in either Japan's Nippon Professional Baseball Organization (NPB) or the Korean Baseball Organization (KBO) before coming over after they reached free agency and wanted to try their game at the best baseball league in the world. Oh has played in both leagues. The large majority of those players, like Oh, are also relievers.
At his older age, Oh is clearly making up for lost time. As usual, I'm writing this the day before you read this, so this doesn't count his inning and a third he pitched tonight, err, I mean yesterday. Going into yesterday, Oh is tied for 3rd-7th with five relievers at 35 appearances. He's been quite the productive pitcher over that time frame, to the tune of a 1.42 FIP and 1.2 WAR, 3rd and 6th among qualified relievers respectively. That's out of 163 relievers, so top 2% and 4%.
Oh's performance isn't only elite relative to other 2016 relievers; his season on a rate basis has so far been one of the best rookie reliever performances on record. Here's the top 10 of all qualified reliever rookie performances from 1990 on (around when most teams adopted the modern bullpen, influenced heavily by Tony LaRussa), ranked by FIP-:
Of course, Oh might not keep this up. The fact that there's three relievers from 2016 on this list, and only one other year with multiple entries should clue you into the fact that at this stage of the season, we shouldn't assume a historic rate will hold up the rest of the way. For instance his HR/FB rate, at a puny 3.3%, is probably a bit lower than what he'll post going forward. He's certainly tough to square up, with three plus pitches, but probably not to that degree. He's doing it now though, which is pretty great in itself. Notice also that the players in front of him all had (or in the case of Deolis Guerra, has) short inning totals relative to a full season. Oh seems likey to finish the year with a higher WAR total than the three seasons in front of him in FIP-, just having 3+ more months to add on.
In the first 68 games of the season, Oh has thrown 35 2/3 innings. At that rate, he's on pace for 84 innings pitched. If he continues to pitch at the pace, in terms of quantity and quality, he'd also crack the rank 5th in WAR among rookie relievers since 1990:
*The players who don't have xFIP- listed played in an era before batted ball stats were recorded (pre-2002). Since FB% is used to calculate xFIP, it can't be calculated before then.*
Some pretty impressive names on their, plus one infamous racist from my adolescence that I can't help but laugh at upon seeing his name. It's also neat to see Trevor Rosenthal here, if nothing but a reminder of what he's capable of. Rosenthal's rookie season is second in WAR among Cardinals relievers since 1990, topped only by Jason Isringhausen's 2002 season at 2.5 WAR. Interestingly, Izzy's 2006 is also the fourth worst reliever season by FIP-. Oh is on pace to beat Izzy's 2002, and is so far is ahead of him in FIP-:
This is also a second reminder of what Trevor Rosenthal is capable of. Trevor and Lee Smith are the only pitchers to appear twice on here. Oh is on pace to beat them all though.
What makes him so good? I'd say it has to do with the fact that he has three plus pitches. A Beta feature at Brooksbaseball.net describes his pitch mix much better than I could:
His fourseam fastball generates an extremely high number of swings & misses compared to other pitchers' fourseamers and has essentially average velo. His slider generates an extremely high number of swings & misses compared to other pitchers' sliders, has less than expected depth and has primarily 12-6 movement. His change generates a high number of swings & misses compared to other pitchers' changeups and generates a very high amount of groundballs compared to other pitchers' changeups.
The Whiff/Swing on his fastball, slider, and change goes 31%, 42%, and 51% respectively. I'd like to be able to tell you how rare that is, but BrooksBaseball doesn't have a leaderboard or anything like that. I can tell you though, that he has the 5th lowest Contact% among qualified relievers this year.
When we shift to talking about contact on pitches in the zone (Z-contact%), he's been the single best reliever in the game, with a 72.7% rate. That's pretty important to me: hitters aren't exactly just chasing pitches in the dirt, they're having the a lot of trouble just making contact on strikes. Khris Davis is the only MLB hitter with a lower Z-contact% than the MLB average when facing Oh. When considering contact outside the zone (O-Contact%) it drops to 48.3%, but that "only" ranks 21st this year, not quite elite territory.
With the Cardinals' usual bullpen ace having trouble reaching the strike zone and getting swings out of the zone, Oh has more than picked up the slack. If Rosey was having a similar season to 2013 or 2015, this post may have been about how dominating of a pair Rosenthal and Oh are. There's still that possibility down the line though, as Rosenthal's stuff is still there, the command is just off. For now, we'll just have to deal with watching one of the finest rookie reliever seasons of the modern bullpen era, and one of the best performances from any reliever in a Cardinals' uniform.