Picking pitchers is a surprisingly difficult proposition. There aren't really clearly defined roles or necessary considerations the way there with position players. Pitchers pitch, largely, and while some may excel in certain things and in certain cases. By and large, a great pitcher is a great pitcher. Rivera, arguably, is an exception to this rule -- his one perfect pitch seems to have made him a genius reliever but not such a great starter. Who knows, though, what would have been had he stayed in the starter role. That cutter, with a decent sinker and changeup? Not a starter I'd want to face.
The whole point of a bullpen is that it can be used in anyway you imagine. So it's useful to have flexible pitchers. As such, I'm labelling one of my slots "swingman" and aiming it for the sort of pitcher that is both a first class starter and a shutdown reliever. Few pitchers have shown the flexibility to do both.
Selection: Satchel Paige
It may be that Leroy Robert "Satchel" Paige was the greatest pitcher that ever lived. Anecdotally, the case is strong. I'll let a Hall of Fame quality storyteller relate Paige's fastball:
I'm going on faith here, obviously, but think about this: Satchel Paige became a legendary pitcher even though (1) He spent his prime playing in Negro Leagues where few media members saw him; (2) He really did not throw anything but a fastball. The second part is what's so intriguing: Paige named his pitches -- Bat Dodger, Midnight Creeper and so on -- but best anyone can tell they were all fastballs thrown at various speeds and with remarkable command. When Paige was asked about how he changed his grips, he would scoff and say he just grabbed the baseball and threw it. I don't know that it was quite THAT casual, but I do think Paige basically threw fastballs and only fastballs until later in his career. Basically every player who faced that fastball -- from DiMaggio on down -- said it was unlike anything they had ever faced, that it was on top of them before they could react, that it was by them before they could blink. And his control was exalted; the story went that he would warm up by throwing fastballs over stick of chewing gum.
I sometimes wonder, by the way, if Paige's fastball was a lot like Mariano Rivera's cutter.
The data isn't bad either. In 476 innings pitched in the majors -- a pittiance that at least demonstrates the injustice of segregation -- Paige posted a 3.29/3.27/81/81 (ERA/FIP/ERA-/FIP-), all over the age of 40. He mixed in starts and relief apperances, demonstrating his swingman ability at an age many greats are long out of baseball.
There is also the Negro league data to consider. Paige allowed an average of 3.22 runs per 9 innings (not earned runs, but all of the runs, regardless of fielding mistakes) across almost 1300 innings pitched in the Negro Leagues. His strikeouts per 9, 8.1, and his walks per 9, 1.7 suggest a pitcher with excellent stuff and fine control.
As Paige was primarily a fastball pitcher, I'd likely prefer using him in a relief and long relief role to avoid giving opponents too many looks at his (many different) fastballs. But I have faith in his ability to start as necessary and so he gets my nod at swingman.
Former Cardinal John Smoltz originally occupied the slot Billy Wagner now has, when it was my swingman spot. Though I could not resist or avoid the Wagner temptation, Smoltz has a deserving case for almost every role a right handed pitcher can be shoehorned into. Switched back and forth between starter and closer through out his Braves career, Smoltz never lost his effectiveness, even in his unlucky final season, where a 6.35 ERA belied a 21.2% K rate and a 5.2% walker rate, good for a 3.87 FIP. Smoltz was a very good to great starter and an utterly amazing reliever, particularly his 2003 year where he posted a 1.12/1.54/25/35 pitching line in 64 innings. Not even Mariano Rivera had a peak that high as a reliever. Smoltz's best year as a starter probably came in 1996: 2.94/2.64/69/60 with 253 innings pitched. Across his 21 year career, Smoltz averaged 3.33/3.24/81/78.
Smoltz's shutdown/meltdown ratio is worth noting too, 131/20. That's mindboggling high. It's over 6 to 1, and even Rivera only manages just under 5 to 1. Smoltz probably represents one of the best arguments against Rivera as "greatest reliever/closer of all time." Oh, and Smoltz's bat was (relatively) decent as well, with Fangraphs putting him at 7.5 batting Wins Above Replacement.
An incredible pitcher with amazing peaks as both a reliever and starter, Smoltz makes a great swingman choice. Maybe we could go back and make this a 26 man roster.
Knuckleballers seem like a natural choice for a swingman. Their arms are effectively rubber, allowing them to plug into the rotation as necessary and the shear alienness of their pitches is only exacerbated by coming in as relief for a fireballer. Hoyt Wilhelm is the prototypical swingman knuckleballer, with plenty of innings in both relief and as a starter. For his career, wilhelm produced a 2.52/3.06/68/81 line, and it's worth noting that fielding independent metrics like FIP may have issues with knuckleball pitchers. Either way, Wilhelm was a durable, flexible and effective pitcher and the best choice for a knuckleballer if you require one for you team. Given the heat the rest of the team is throwing, I'd bet Wilhelm would be even more effective.