Stunt men exist so that actors in movies don't have to put themselves at risk of injury. It's a simple financial calculation, if an actor gets hurt, productions can be delayed and that costs money. Some actors still do a lot of their own stunts themselves, but Bill Hader needed to call in his own stunt double for IT Chapter Two after he apparently injured himself...while running in a straight line.
One would not necessarily think to call running a "stunt," but for Bill Hader, that was apparently the case. The IT Chapter Two actor revealed on The Tonight Show Starring Jimmy Fallon, that he actually pulled his groin muscle, while doing nothing more than running. According to Hader...
No, so like James McAvoy does his own stunts. He can like, run up and jump off of things, do a bunch of crazy things. There’s a part where I had to run from the clown, and I ran four feet and pulled my groin muscle. I was like, ‘Oh!’ and I just fell. They had to get my stunt guy just to run. The stunt dudes are so stoked, like, ‘What am I doing brah?’ And the guy was like, ‘I’m just gonna run? Are you serious? Like miles right? Am I getting hit by a car?’
Apparently the injury was serious enough that he had to see a doctor during the production. IT Chapter Two certainly involves a lot of running, so it's possible Hader had to miss out on a lot of it due to hurting himself.
While Hader received his injury while simply trying to run, McAvoy's came during a scene where he fought Pennywise, which likely makes for a much more interesting story. If you're going to hurt yourself on a movie set, it's best to have a cool story to go with it.
You can check out Bill Hader's full comments about his injury in the clip below. He also discusses his thoughts on being tapped directly by Finn Wolfhard to play the older version of Richie for the new movie.
Most of us can probably relate. If you've ever hurt yourself to any degree while doing something you didn't think twice about, then you've been there. On the plus side, Hader's stuntman got more work to do, even if he was potentially unimpressed with what he needed to do.
Watch Bill Hader, and the rest of the grown up Loser's Club, do lots of running away from the scary clown when IT Chapter Two hits theaters on Friday.