Major League Baseball umpires: Danger zone ahead?
MLB, Official Information, Umpires
Umpire (baseball) - Wikipedia
MLB notes: Umpires wear white wristbands to protest 'abusive player behavior' - Los Angeles Times
Umpire (baseball) - Wikipedia
Baseball Umpires Don't Get Overtime. Does That Affect Extra Innings? : NPR
Major League Baseball umpire loses appeal of discrimination lawsuit
MLB, Official Information, Umpires
Don't Ignore The Signs! How To Become An MLB Umpire.
As MLB moves toward using 'robot umpire,' getting strike/ball calls right is the goal
MLB umpire job responsibilities
Don't Ignore The Signs! How To Become An MLB Umpire.
Umpire (baseball) - Wikipedia
MLB umpire job responsibilities