Robert Downey Jr. broke his ankle on the set of Iron Man 3 while acting like Tony Stark in real-life. Accidents happen on sets all of the time. However, when the star of the movie is participating in the stunts, the accidents are often much worse since production has to be stopped. Tom Cruise famously broke his ankle on the set of Mission: Impossible film Fallout and the movie came to a screeching halt for months, leaving some crew members without work.
As for the Iron Man 3 incident, Robert Downey Jr. also shut down the production. Guy Pearce played a large role in the movie as the villainous Aldrich Killian and was recently interviewed. He spoke about his time in the MCU and working with Downey Jr. He even went into detail about how the Iron Man actor broke his ankle. Pearce had this to say.
"Robert broke his ankle in the middle of that film, 'cause he had to a stunt where he had to jump from one platform down to another platform and be on a cable. They went to rehearse it, and he said, 'No, I don't need to rehearse it,' and he jumped, and the guy holding the cable wasn't ready or something, and he landed hard, and he broke his ankle, so the film sort of shut down for 5 or 6 weeks."
It sounds like Robert Downey Jr. was channeling his inner Tony Stark when he decided to do the aforementioned stunt without rehearsing it first. Whatever the case may be, it was probably a tough lesson to learn for the actor, who is now officially finished with the MCU, at least for now. There's always a chance he could come back at some point for a cameo, but it seems his days of performing wild stunts are over.
Tony Stark sacrificed his life to save the universe in Avengers: Endgame. MCU fans knew some deaths were coming, but did not expect there to be anymore after Black Widow made her sacrifice on Vormir. Robert Downey Jr. and Chris Evans had been frontloading fans for about a year that their time in the MCU was coming to a close, though many were hoping it was just going to be superhero retirement and not death.
While the Iron Man 3 production was shut down for 5 to 6 weeks, all MCU projects are now on hold with the rest of the entertainment industry due to the coronavirus. It's unclear when any of these projects, including The Falcon and The Winder Soldier, will be able to commence, but it looks like it's going to be a while. For now, MCU fans have a decent amount of time to head back and watch Iron Man 3 to see the stunt that broke Robert Downey Jr.'s ankle, but rehearsed and pulled off clean. You can check out the interview with Guy Pearce below, thanks to the GQ YouTube channel.