Simmons was cited on suspicion of assault after he slapped a 6-foot-2, 250-pound ultimate cage fighter across the face Wednesday night at the Sky Harbor International Airport terminal, the Arizona Republic reported.
The fighter reportedly said: "Hey, look everybody, it's Richard Simmons. Why don't you drop your stuff and start dancing to the oldies?," said Phoenix police Lt. Lowell Spalla.
"Simmons approached him and said, 'You shouldn't make fun of people who have issues,' and then he slapped him," Spalla said.
Simmons, 55, is known for his boisterous personality and outlandish exercise videos, frequently set to music from the 1950s.
Simmons was cited and released before boarding his flight.