First off, let's talk about who actually won. Mariano Rivera, to absolutely no one's surprise, took the award this year. Now, in a vacuum, this isn't a crime. Rivera tore a ligament in his in knee while shagging flyballs during batting practice in Kansas City on May 3, 2012. He missed the rest of the season. The fact that Rivera, now 43 years old, returned from such a traumatic injury at his age and put up one final excellent season (2.11 ERA, 3.05 FIP, 1.5 fWAR) in his Hall of Fame career is indeed amazing. Was it really the comback most worthy of celebration though? I don't think so. I suspect that the voters wanted to give Rivera one final award in his last season. He probably would have won this as long as he took the mound at all this year, regardless of how he performed or what anyone else in the league did.
So, who do I think should have won?
There is an excellent case for John Lackey to win, although he is my second choice.] Lackey was horrible in 2011 (6.41 ERA, 4.71 FIP) then missed all of 2012 with Tommy John surgery. No one expected much of anything from him in 2013. Even simple mediocrity would have been a pleasant surprise to Red Sox fans. Instead, Lackey was fantastic (3.52 ERA, 3.86 FIP, 3.49 xFIP) and was a rock in a Boston rotation that, at times, looked shaky. He came back from being a player who was booed frequently in Fenway to receiving a standing ovation in Game 6 of the World Series. If I had a ballot, Lackey would have placed second.
My first place vote would have gone to Scott Kazmir of the Cleveland Indians. To me the Comeback Player is an award that should be just as influenced by the story as the results on the field. While Kazmir's results weren't flashy--his 4.04 ERA and 2.5 fWAR made him more of a mid-rotation starter, although he had an very good xFIP of 3.36--his story is what really sells him. Rivera and Lackey both came back from injuries. Kazmir came back from his career being over. After putting up both horrible and injury-plagued seasons in 2009-2011 (FIP by year: 4.26, 5.83, 18.03--one start, but pounded in the minors), the former Tampa ace was out of Major League Baseball as of June 15, 2011. He spent the rest of 2011 and all of 2013 pitching for various independent Dominican and Puerto Rican teams. Players almost never come back from that point. However, the Indians heard that his fastball velocity had returned and took a chance on him. He rewarded their gamble by helping the Tribe secure a Wild Card berth.
Scott Kazmir returned not merely from injury, not merely from ineffectiveness, but from oblivion. He is my Comeback Player of the Year.