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1.
when an umpire in a sporting event makes a wrong call obvious to the entire audience.
Man, Lincecum got umpjacked! That was definitely a strike!
by Baseballdreams21 June 03, 2010
 
2.
Ump jacked is when an umpire, primarily the home plate umpire is missing calls for the pitcher or makes a very bad 3rd strike call on a batter on an obvious ball. Also when pitcher is getting obvious strikes called balls by umpire.
Detroit Tigers pitcher Armando Galarraga, got "Ump Jacked" when Jim Joyce's blown call at first base on potential last out of the game, cost him a perfect game.

David Wright got Ump Jacked on that 3-2 pitch.

Eric Gregg Ump Jacked Atlanta Braves in 1997 National League Championship Series game 6. He called every pitch a strike for Marlins. Lead Braves to have to hack at any pitches by mid game, even obvious balls. Eventually led to him getting dismissed by major league baseball when they purged several bad umps from their ranks in the early 2000s.
by JAX8 June 22, 2010