The incident happened during a 13-and-under game early this month in Branchburg, the US Amateur Baseball League said on Facebook.
The coach who was "built like a linebacker" was apparently seen drinking in between games, and ejected after repeatedly arguing with the umpire, officials said.
Upset about a call the umpire with more than 35 years of experience made, the unidentified coach apparently went up to him and socked him in the face.
"The umpire's jaw is fractured in 2 places, wired shut and requires extensive dental surgery," the post says.
"The coach fled the scene before police arrived like a coward. Even as police and EMT's were providing medical attention to the umpire, other parents from the same team were heard shouting expletives at the umpire and saying things like 'He deserved it.'"
Mike Kolesar, General Manager of the Gamers Baseball/Softball Academy, said he's never seen anything like this in his years of experience.
"What are we doing?" he said in a video shared to Facebook. "What are we teaching these kids? And the parents of that group screaming out he deserved it? How bad can it be?
"We’ve got to be better."
Branchburg police said only that the incident was under investigation, and the coach and his team have been banned from the league, officials said.
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