Local media outlets report that 34-year-old Craig Lawson of Courtland, Ont., entered his plea Wednesday in Genesee County Court.
Authorities say Lawson punched Jason McNeil of Tuscaloosa, Ala., during the July 5 concert at Darien Lake Performing Arts Center in the town of Darien, 40 kilometres east of Buffalo.
Police say the attack was unprovoked.
McNeil was in a coma at a Buffalo hospital for two weeks after the beating and remains hospitalized.
Lawson was released after posting $10,000 bail.
A fundraiser was started for McNeil, his wife and two daughters. Kid Rock donated $5,000.