bench jockeying
arguing a call at first base (19 ejections)
arguing balls and strikes (59 ejections)
fighting the other team's pitcher on the field
arguing a called third strike (16 ejections)
spitting on an umpire 
arguing a balk call (10 ejections)
arguing a checked swing (12 ejections)
arguing a call at second base (7 ejections)
protesting a bat throw at a pitch-out during a steal
arguing a call at homeplate (4 ejections)
taking issue with an umpire saying something to one of his coaches
protesting a balk non-call
arguing a hit by pitch call (3 ejections)
his pitcher throwing a brushback pitch after a warning
protesting the condition of the field
arguing an interference call (2 ejections)
throwing a helmet at the dugout steps that bounced onto the field
protesting an order to speed up the game
arguing a call at third base (3 ejections)
arguing a fair/foul call
bumping an umpire (3 ejections)
arguing an interference non-call (3 ejections)
arguing about the catcher's box behind the plate
protesting an intentional hit by pitch (2 ejections)
protesting that his runner was not allowed to advance 1 base
arguing an automatic ball called on his pitcher
pointing to the dirt while arguing a fair/foul call
protesting the delay to turn on the field lights
arguing a confusing call on a pitch during a stolen base
throwing his hat while arguing a call at first base