Raisner was filmed by television cameras striking the horse, called Saint Boy, with her fist after he refused to jump fences for Germany’s Annika Schleu in the showjumping round of the women’s modern pentathlon event on Friday.
Schleu struggled to control the horse throughout the round, and was in tears.
Schleu, who finished fourth at the Rio Games in 2016, had been leading the field before the equestrian round. She was eliminated from the showjumping element and finished the entire event in 18th place.
In a statement released online Saturday, the International Modern Pentathlon Union said it had “given a black card” to Raisner “disqualifying her from the remainder” of the Tokyo Games.
Its executive board had “reviewed video footage that showed” Raisner “appearing to strike” the horse “with her fist,” it continued.
“Her actions were deemed to be in violation of the UIPM Competition Rules, which are applied to all recognized Modern Pentathlon competitions including the Olympic Games,” the statement added.