Hayden Penn: The former Oriole was out of options this year, and Baltimore dealt him away to Florida (for another optionless former prospect, shortstop Robert Andino) when they decided they didn't have room for him in their bullpen. Given his major league track record it's no wonder. Penn has a career 9.31 ERA and 2.03 WHIP, with a 26:34 K:BB ratio and 84 hits allowed, in 58 big league innings -- absolutely atrocious numbers by any standard.
His minor league numbers, however, are a different animal. Penn landed on top prospect lists when he posted a 120:37 K:BB ratio in 110.1 Double-A innings as a 20-year-old in 2005, then came back the following season and racked up an 85:27 K:BB ratio in 87.2 Triple-A innings. In both years he received ill-advised major league call-ups and got rocked (leading to his being out of options in 2008). 2007 and 2008, however, did not go well at any level as he battled through first a bone spur in his elbow, then some shoulder soreness.
Even at his best Penn never possessed awesome heat, instead relying on a big-breaking curve and plus change-up to fool minor league hitters. The arm troubles knocked a couple of mph off that mediocre fastball which, in turn, reduced the effectiveness of his change and left him very, very hittable. His first outing of the season for the Marlins, however, offered some hope that he might have his best stuff again. He struck out four Mets in two innings (although he also allowed four hits and three unearned runs) and while it's not the most reliable indicator MLB Gameday shows that Penn was consistently in the 90-93 mph range with his fastball, with his change in the 81-85 mph range. Add in the big mid-70s curve and you've got a repertoire capable of some major league success, control and command (and health) willing.
Andrew Miller is slated to be Florida's #5 starter (they haven't needed a fifth starter yet, so Miller's been working out of the bullpen) but he's got some health issues and spotty major league performances of his own, so he's no sure thing. Penn will work at the back end of the Marlins bullpen for now, but if he keeps getting K's and Miller struggles when his turn finally comes around Penn could easily be the player they turn to. Especially in a keeper league, if you've got a reserve spot for a spec pitcher you could do a lot worse.