Eric Seidman from, well, all over the internet (in this case Brotherly Glove), has written up a post about the Phillies potentially looking at Koji Uehara to strengthen their bullpen before the trade deadline, and asked for some info. about the O's reliever. Having written up some stuff, I thought it worthwhile to share fully (and expound some).
Going back to before the 2009 season... the Orioles made their first foray into the Japanese market, signing then 33 year-old right-hander Koji Uehara to a two-year, $10 M contact. Koji came to Baltimore in part because they were the only team willing to give him a chance to start, and I was a big fan of the deal - relatively low risk, medium reward.
Koji had trouble staying healthy in '09 (only totaling 66.2 IP), but when he was on the mound he was effective; 4.05 ERA, 3.56 FIP, 4.42 xFIP. The following year the O's moved him to the bullpen, and the same thing occurred - when he pitched (44 IP), he was really good (2.86 ERA, 2.40 FIP, 2.70 xFIP).
Koji totaled 3.1 fWAR and 2.3 brWAR (which has a higher repalcement level, so they're not so far apart) in those first two seasons, making him easily worth his contract even if he didn't much all that much. The O's brought him back for 2011 for just $3 M, and he's been both healthy and effective.
To say Koji is the team's best reliever seems obvious, but he's actually one of better ones around anywhere; 2.13 ERA, 3.01 FIP, 2.46. His walk rate of 1.9 BB/9 is actually the highest of his career (yeah, he's got good control). He's once again striking out a ton of batters (11.8 K/9). In fact, his strike-out rate over the past two seasons is the fourth highest in the majors (min. 70 IP). How is he managing that?
His stuff does not look terribly impressive. His fastball rarely touches 90, it doesn't move a ton, and it's of the four-seem variety. He tends to throw it up in the strike-zone, which results in a lot of flyballs (and thus he's sometimes prone to giving up the longball). That doesn't sound like the main pitch of a guy who striking out over 11 per nine in his relief career.
Complementing the heater is a pretty wicked splitter - it looks just like the fastball but comes in a few mph slower and actually has some good movement. Because he throws the split so often, I imagine it's tough for batters to know where/when to swing until the ball's already well on the way to home plate. That deception (plus his motion, which may contribute to the effect), I think, is what has allowed Koji to K so many batters out of the pen. Only Mariano Rivera has gotten batters to expand the zone more the last two years, as far as inducing batters to chase pitches is concerned (according to FanGraphs).
When hitters were seeing him for the first time in a given game when he was a starter, he was similarly overpowering (9.0 K/BB, while striking out 25% of the batter he faced). And, of course, as a reliever, all batters are seeing him for the first time (8.1 K/BB, while striking out 28% of the batters he's faced).
His stuff ends up being much more effective when looked at as a whole than the individual pitches might indicate. Not only does the split get set up by the fastball (38% whiff rate for '10 and '11 on the spitter) - not unusual - but it works the other way too (25% whiff rate on the fastball*). The first few times you see Koji throw an 88 mph fastball right by a big league hitter it's a little jarring - the batters react like it's really going 98. Then it just becomes amazing.
* Fellow BtBer and all-around good guy Lucas Apostoleris checked it out for me, finding that for pitchers whose fastballs averaged under 90 mph, Koji had the highest whiff rate on the pitch in 2010. And he's been even better with it this year, so it wouldn't be at all surprising if he's #1 again.
So a healthy Koji Uehara is pretty clearly a very good reliever. Over the past two season he's accumulated 2 fWAR out of the pen. Second on the O's is Jim Johnson at 1.5 fWAR. Then things drop off all the way to David Hernandez (who isn't even on the team anymore) at 0.6 fWAR.
Given that, I think the Orioles would be loath to part with him. They gave guys like Mike Gonzalez and Kevin Gregg multiple year contracts at higher than advisable salaries, so it seems like they give a fair amount of weight to having a "strong" pen.
Realistically speaking, he's maybe a 1 win player for the rest of the season on a very reasonable contract (and should provide the team a draft pick or two when he becomes a free agent). That's worth a solid B prospect, I think, but the O's might be looking more at the Matt Capps - Wilson Ramos swap from last year as a basis to unload Koji. And as much as I like having Koji come out of the pen as the team's relief ace, it would probably be for the best to deal him if there was some real talent coming back.
Stats: ERA, FIP, xFIP, K/9 & BB/9, PitchFX, WAR