The Rangers are apparently going to give Neftali Feliz a chance to start in Spring Training. As dominant as he's been in the closer role, his success as a starter will largely be determined by the effectiveness of his secondary pitches. Last year, Feliz relied on his fastball 83% of the time. Obviously, he will have to adjust his approach as you can't get by throwing that many fastballs in a starting role.
Feliz throws a curveball (often mistaken for a slider) and a changeup. His K-Rate on his secondary pitches was around 40.4% last year, which put him into the 92nd percentile for all soft pitches thrown in the majors in 2010. And his contact rate of 61.7% put him in the top 87th percentile.
Of course, he only threw his secondary pitches 17% of the time last year, making it more difficult for batters to identify and adjust to them in brief stints. It will be interesting to see how Feliz changes his approach as a starter, and how effective those secondary pitches can be when utilized more often.