This story comes from a wrestling documentary called Hitman Hart: Wrestling With Shadows. In the 1990s, Bret Hart was working a match against an opponent who went by the hopefully fake name of Dino Bravo. At one point, Dino was supposed to bump Bret off of the side of the ring and into the steel railing. It's one of those wrestling moves that looks like it'd leave you in the hospital, but if you know what you're doing, you're fine. And Hart had done this many times before.
The wrestling equivalent of putting toner in the copier.
This time, however, Bravo bumped Hart a little too hard, sending him off balance. When he landed on the railing, he broke his sternum and most of his ribs.
Now in pro football, if this happens, the whole goddamned game comes to a stop. The guy writhes around on the ground and they bring out a stretcher and a dozen trainers. But in pro wrestling? They've got a script to follow. They've got kayfabe.
Hart laid there in pain for quite some time as the referee and Bravo waited for him to get back in the ring (as per the script). They had no idea he wasn't acting. Playing his own part, the ref began counting Bret out (in wrestling, if the referee counts to 10 while you're out of the ring, you lose), and Dino knew this wasn't how the match was supposed to end. He didn't know that Bret had basically lost his ability to draw breath into his lungs.