The 18-year-old Harper, the No. 1 Draft pick in 2010 and the No. 2-ranked prospect by MLB.com, was tossed after a called third strike ended his at-bat in the bottom of the seventh inning of the Harrisburg Senators' 3-1 home loss to the Richmond Flying Squirrels.
Harper, a left-handed hitter who was facing a left-handed pitcher, believed the full-count pitch to be outside, which replays showed it might have been.
Harper was moving up the first-base line when home-plate umpire Max Guyll made his call, and Harper responded by spiking his helmet before turning toward Guyil and using his foot to draw a line in the dirt on the outside part of the plate -- seemingly in an effort to show where he believed the pitch missed. He moved closer to Guyll and shouted at him until one of the Harrisburg coaches came to pull him aside.
Both clubs were unhappy with Guyil's strike zone, The Patriot-News of central Pennsylvania reported.
"There were a couple of pitches I just thought were off the plate," Senators manager Tony Beasley, who was also ejected trying to separate his star from the argument, told the newspaper. "I mentioned that to [Guyll] earlier in passing. But the pitch on Harper I just disagreed with, and obviously Harper did, too.
"It's a 1-1 ballgame, and obviously I don't want [Harper] to do that. That's not going to keep him in many ballgames, but that was just his reaction tonight in what he thought was a successful at-bat ending in a walk but ended up as a strikeout. He just allowed his emotions to get the best of him. It happens sometimes."
Harper has not been a stranger to controversial moments in his young career. While with Class A Hagerstown in June, he blew a kiss to Greensboro pitcher Zachary Neal after homering. And in June 2010, when Harper was still an amateur, he was suspended from the Junior College World Series for two games following an ejection.
Harper's statistical performance has been star-caliber since he turned pro. Across two Minor League levels this season, he is hitting .297 with 16 home runs, a .390 on-base percentage and a .504 slugging percentage. Double-A has appeared to slow him some, though: he's batting .248 in 31 games in the Eastern League, which is typically populated by much older players.