Guess the Prospect!

Guess the Prospect!
    The winner of Guess the Prospect! gets to pick the next subject for a Player Profile/Post-Hype Analysis.

    I am a pitcher. An outstanding athlete as an amateur, I grew up in a cold-weather state. I threw hard and was projectable, but was very raw, and for this reason I was drafted between the fifth and 15^th rounds rather than going earlier in the draft.

     I struggled in my first look at rookie ball, improved in my second year there, then emerged as one of the best pitching prospects in baseball with a  tremendous season in Low-A in my third year. I zoomed through the minors in my fourth season and reached Triple-A, holding my own. I made the majors for the first time in my fifth pro season, then bounced between Triple-A and the majors for two more years, never quite finding my rhythm.
    I finally earned a full-time rotation spot in my eighth professional season, but I was absolutely terrible and one of the biggest enigmas in baseball. I did have a good arm and I worked hard, but starting just didn't suit me. At age 27 I converted to relief, pitched better, and began a very long trek as an erratic but occasionally successful relief pitcher.
    Who am I?