If a movie script includes a scene set at a huge public gathering, like a sporting event or a parade, that presents a challenge for the production team. There are lots of ways a film production can execute a crowd scene, but none of them are cheap. A production could use thousands of extras, but those extras all have to be paid. Modern movies can rely on CGI to create virtual crowds, but convincing visual effects can cost tens or even hundreds of millions. One company even lets movie productions rent inflatable plastic crowd members, but those don't come free, either.
Often, the simplest and cheapest solution is to film at a real-life event. But while this might keep a movie's budget low, it can also create a whole slew of logistical headaches for the production team. Here are some movies that filmed at real-life events, and how they pulled it off.