Jeff Sackmann has an interesting article at Hardball Times, "Relievers in the Rough." A commonly stated axiom in major league baseball is that the best relievers are former starters. And we can certainly think of many examples, including such luminaries as Billy Wagner and Mariano Rivera. But not all starters make good relievers, and it may be a subjective "hit or miss" exercise to determine whether a pitcher's best use is as a starter or reliever.
Sackmann first set out to identify the characteristics which differentiate a good reliever from a starter: pitching in short bursts, large platoon splits, and pitching well out of the stretch. He then defined how each characteristic could be measured statistically: performance difference between first and second time through the batting order; platoon splits versus LHB and RHB; and performance difference with runners on base, since that means the pitcher is pitching from the stretch. He then ranked minor league starting pitchers on these criteria in order to determine those who are the best candidates for conversion to relief pitching.
An ex-Astros' minor league starter, Chad Reineke, was ranked as the best candidate for relief pitching. Reineke was traded by the Astros to the Padres for Randy Wolf. Reineke had marginal success as a starting pitcher for the Padres, and was signed by the Oakland A's organization.
The only Astros' minor leaguer who made the list is Gustavo Chacin. Some of you may not be familiar with him as an Astros minor leaguer, because he actually pitched for the Phillies' organization last year and then signed with the Astros this offseason. Chacin, at one time, was a good starting pitcher for the Blue Jays, where he undoubtedly worked with the current Astros' pitching coach. He had arm problems and underwent shoulder surgery in 2007. He has pitched in the minors subsequent to recovering from the arm surgery. Based on Sackmann's study, Chacin is among the 17 minor league starters who seem like the best candidates for conversion to relief pitcher.
Although the Astros appear to be well stocked with relief pitchers, Chacin has one advantage: he is lefthanded. The Astros have one LH relief pitcher, Tim Byrdak. Wesley Wright is a lefty, but it unclear whether he will continue to be groomed as a starter or placed in the bullpen this season. Ed Wade's most recent quotes left open the possibility that either starting or relieving could be in Wright's future. If the Astros like Wright as a starter, I could see the possibility that he spends time in Round Rock continuing to hone his skills as a starting pitcher.
Neither Wright nor Byrdak have the platoon split you would expect for a LOOGY. Both Wright and Byrdak were more effective against RHB than LHB (OPS against--Wright, RHB .853; LHB .924; Byrdak, RHB .640; LHB .700). Chacin, on the other hand, shows distinct platoon splits. Last year in AAA, he was 1.5 runs/9 better versus LHB than RHB. (Chacin FIP vs. LHB, 3.38, vs. RHB, 4.87) As a Blue Jays' pitcher in the major leagues, he also exhibited a noticeable platoon splits (OPS against: .795 vs. RHB, .728 vs. LHB). His major league splits also seem to support the idea that he pitches better from the stretch.
My conclusions: maybe Chacin could surprise us as an effective lefty-specialist out of the bullpen. Chacin has an invitation to spring training, and at the time, the media portrayed him as a candidate to compete for a rotation slot. However, many competitors are now available for the rotation. Perhaps Chacin should be tried out as a lefty relief candidate this spring.