I liked this significantly more than I expected. I attribute this to a good directing job by Clint Eastwood.
I knew the story going in: Fat rent-a-cop Richard Jewell spots an unattended backpack one evening at the 1996 Summer Olympics in Atlanta, alerts everyone, tries to move people away. The backpack exploded, but thanks to Jewell's efforts, many lives are saved. Unfortunately, Jewell becoems the FBI's designated suspect, a fact that's leaked to the press. Which subsequently makes Jewell's life hellish.
What's unexpected is that the movie makes Jewell (well-played by Paul Walter Hauser) into an actual person: he's a cop wannabe, but sports some bad-cop habits: bullying and authority-exceeding. And he's not that smart, either. (Sorry, Richard.) Despite all that, we're sympathetic. Because he's basically a good guy.
Jon Hamm plays FBI agent Shaw, and he's everything Jewell's not: smart, good-looking, by the book. But he's the bad guy here, because once he gets the idea that Jewell fits the "hero perp" profile, he can't let go, and he can't let inconvenient facts—like there being no evidence whatsoever—dissuade him.
Sam Rockwell is also excellent as Jewell's lawyer.