Callahan has settled down since his first 4 appearances in AA. Over his last 7 games and 9.2 innings, he has 10k/3bb and an era of 2.79. He has given up 2 HRs though. Hitters are slashing .152/.222/.394 with a BAbip of .143 in that time. He coasted through AA, having 13ip, 0bb/20k and a 0.62 WHIP. Still just 22, the move to the bullpen has definitely helped his career and has seen him rise through the system quite quickly.