Prior to his coaching career, he played in the New York Yankees minor league system from 1979 to 1983. He also played part of the 1983 season in the Chicago White Sox system. A broken arm that year ended his playing career.[citation needed]
Hernandez was then[when?] pitching coach for the GCL Phillies and then the Miami Marlins. In November 2015 he was hired as Minor League pitching coordinator for the Atlanta Braves.[2] On October 11, 2016, Hernandez was named the pitching coach for the Atlanta Braves.[3] On October 15, 2018, Hernandez was dismissed from his duties as the pitching coach for the Braves.[4]
On December 9, 2018, the New York Mets hired Hernandez as their bullpen coach.[5] His time in New York was short-lived, however; on June 20, 2019, he, along with pitching coach Dave Eiland, were fired as part of a staff shakeup.[6]