Perez was just dehydrated and recovered quickly. Moustakas was struck in the ninth inning and shook it off.
"It hit him on a good spot, right on the hard spot of your head. It's where all the pro wrestlers head-butt guys with and all the mean street fighters," manager Ned Yost said.
Because no symptoms were shown, Moustakas was not required to undergo tests for a concussion.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.