There is a very established process when a fan catches a milestone home run, such as Shohei Ohtani's first homer with the Los Angeles Dodgers.
The ball legally belongs to the fan, who is quickly escorted from their seat so team officials can speak with them and work out what it will take for the fan to part with the ball. Sometimes, all it takes is a little signed memorabilia; other times, cold hard cash. Crucially, it is within the fan's rights to take the ball and go home.
This practice goes back decades, but the Dodgers couldn't avoid unnecessary drama when it happened with Ohtani's homer on Thursday.