Why does Joba Chamberlain have a pitching limit?

Answer 1

Joba Chamberlain first came up and was used as a Relief pitcher and mainly became a set-up main for Mariano Rivera and pitching one inning (the 8th). The Yankees wanted to protect such a valuable young pitching prospect so they developed strict rules for how and when Joba could pitch and how long he rested in between appearance. These rules were around when he first came up last year and were named the "Joba Rules" by fans and reporters.

This year the team decided to change Joba back from a reliever to a starter. However in order to protect his arm and health they decided to slowly increased the amount of pitches he threw. Thus he made appearance with 30 pitches allowed and a start where the limit was around 70 pitches.

Basically the Yankees are limiting Joba's pitches in an attempt to prevent him from tiring out his arm and trying to get him used to throwing as many pitches as a starter.