One of the most beloved scenes in Back to the Future Part II came with a heavy price. When Biff (Thomas F. Wilson) and his crew chase Marty McFly (Michael J. Fox) on hoverboards, several of them burst through the windows of the clock tower.
The stunt was supposed to be relatively straightforward - the performers would swing on wires to generate momentum, then smash through the candy glass windows while a member of the effects team released their wires and dropped them safely onto airbags concealed inside the tower - but it was unexpectedly difficult.
One stunt performer walked away because of how dangerous the scene became, and she was replaced by relative newcomer (and women's kickboxing champion) Cheryl Wheeler-Dixon. While filming the stunt, Wheeler-Dixon didn't go through the glass like she was supposed to. Instead, she hit a pillar and was outside when a crew member cut her wire, causing her to plummet twenty feet onto concrete.
Gary Morgan, another member of the stunt team, recalled the incident later, "I got up and Cheryl was laying on the concrete and the pool of blood by her head was getting bigger." The accident required Wheeler to undergo reconstructive surgery, including having metal plates implanted in her face. It also led to her suing the studio.
The scene, complete with Wheeler-Dixon crashing into the pillar, made it into the film.