The #5 rated MLB prospect the past two seasons, Julio Teheran has quickly risen through the minor league ranks. Last year, at age 20, he spent a full season in AAA, aside from three spot starts for the Atlanta Braves. His AAA stats look sparkling, a 15-3 record with a 2.55 ERA, but there were some causes for concern that have shown themselves this year.
The first problem actually started with his callup to AA in 2010. His walk rate jumped from the 5-7% range up to 10% in those seven starts. While 40 innings is a bit small to make sweeping claims, Teheran's walk rate was at 8% last year, still above previous levels. It is expected for pitchers to be more cautious at higher levels, since the competition is better, but his once-great control has now become average at best.
His strikeouts have also disappeared a bit quicker than expected. After posting a nearly 30% K rate in A and A+ in '10, that dropped to 23.5% in AA and 20.7% in AAA last year and near that value this year. He only struck out 10 of his 87 batters faced in ATL last year, which is concerning since he has the advantage as the new guy. His '11 AAA FIP was 3.06, but could have been much worse if more than 5 of the 123 flyballs would have been hit out of the park in the 144 innings. His GB% is generally around 40%, just a bit below average.
His stuff also does not lend itself to groundballs. His fastball is -4 HOR, +8 VER, which is fairly straight and without great life. The 93 MPH average velocity has been the big reason it's been successful in the low minors. His changeup is -8 HOR, +5 VER, which is a decent circle change with average fade and depth at 82 MPH. His curveball is a 75 MPH sweeper at +8 HOR, -6 VER.
At 21 years old, Teheran has time to polish his approach. He is also wiry at 6'2", 175, so maybe he can become more consistent after gaining some strength. While some are frustrated with his suddenly stalled progress, having a pitcher at his age with his velocity and two decent off-speed pitches is a luxury, and he should still go on to have a good career.