Pestano was probably the Tribe's best reliever in 2011 and 2012, but an injury he suffered shortly before the start of the 2013 season slowed him down that season, and he has been unable to rebound this year. He pitched only 9 innings for the Indians in 2014, in which he gave up 13 hits and showed diminished velocity. He has spent most of the season in Triple-A, where he's posted pretty good numbers, but reports continue to note that his velocity is not what it once was.
Clevinger is a 23-year-old right-handed starter. He was a 4th round draft choice in 2011, and was rated by Baseball America as the Angels #4 prospect, but he missed most of 2013 and has posted modest numbers in Single-A this season, with a good strikeout rate, but somewhat high walk and home run rates, especially since being promoted to High-A in late May.
Clevinger will be assigned to High-A Carolina by the Indians, and he might make 4 or 5 starts for them before the season ends.
Pestano was on the 40-man roster, so his departure opens up a spot there. Feel free to begin speculating on whom the Indians will choose to fill it.