There was a time a few years ago when Bobby Parnell was half-lovingly nicknamed Captain Fastball. He could bring the heat – reaching over 100 mph on the gun – but had problems with control and being hittable. As the now well-known story goes, Jason Isringhausen taught him the knuckle-curve and from that point on, Parnell took off.
After Tommy John Surgery in 2014, he is now back in the majors, and is yet to allow a run in three innings, despite being battered around in his rehab assignments. His velocity is also noticeably down. According to Brooks Baseball data, His fastball sits at 94.1 mph, after it was at 96.1 in his last full-season in 2013. Parnell has also lost two miles per hour off of the curve.
As Mike Fast at The Hardball Times uncovered in 2011, one mph on the fastball at higher velocities corresponds with approximately 0.20 runs allowed per nine innings. Parnell’s RA/9 in 2013 was 3.06, meaning that if the velocity dip holds (which it likely will, as velocity stabilizes very quickly) we can expect that number to jump to the ballpark of 3.46.
That difference might not seem like a large bump on the surface, but with the Mets’ lackluster offense the question of whether you want Parnell to be trusted to get outs in high leverage situations is an important one.
More in the past five years than ever before, pitchers have returned from Tommy John to have success, but there are still risks associated with the surgery. He should still be able to continue to be an effective relief pitcher, but it’s hard to envision him regularly closing games in the future.