Hernandez, 55, worked as the pitching coach for the Miami Marlins from 2013 to 2015. In his first season as Marlins' pitching coach in 2013, Miami posted the lowest team ERA (3.71) in club history. Despite losing staff ace (and 2013 National League Rookie of the Year) Jose Fernandez to injury, the Marlins still posted a 3.78 team ERA in 2014, good for second in franchise history.
Hernandez, who spent two seasons (2011-12) as an assistant coach at the University of South Florida, was with the Gulf Coast League Phillies in 2010, helping lead the club to the GCL Championship with a 3.44 team ERA. In 2009, he served as the bullpen coach for the Cleveland Indians under then-manager Eric Wedge.
From 2006 to '08, Hernandez held the title of pitching coach for the Detroit Tigers. In his first season, the Tigers lowered their team ERA from 4.51 in 2005 to 3.84. He guided a pitching staff that included American League Rookie of the Year Justin Verlander, Kenny Rogers, Jeremy Bonderman and Fernando Rodney to the American League pennant and a World Series appearance against St. Louis.
Hernandez led the Tampa Bay Devil Rays' pitching staff for the 2004 and '05 seasons, and from 1997-2003 he was a coach in Rays' Minor League system.
He spent 11 seasons (1986-96) as Major and Minor League coach with the Angels, serving time with Single-A Palm Springs (1986), Double-A Midland (1987) and Triple-A Edmonton (1988-90). He also served as a roving pitching instructor in 1991 and joined the Angels' Major League staff in 1992. At 31 years of age, he was one of youngest pitching coaches ever. Hernandez remained on the Angels' Major League staff through the 1996 season.
Hernandez played professionally from 1979, when he was taken by the New York Yankees with the 25th overall selection in the draft, until 1983. He began his coaching career in 1985 with the Rookie-level Gulf Coast White Sox.