When Bobby encounters Harry Doolin after Carol Gerber has been assaulted, director Scott Hicks mentions (commentary at 01:27:16) that in both the novel and the screenplay it is a premeditated assault by Bobby who ambushes Harry and beats him up. But Scott Hicks felt the audience would lose sympathy for Bobby unless, instead of being planned, it was self-defense in some way.
Scott Hicks describes (commentary at 01:25:58) the scene where Bobby argues with his mother for turning Ted in to the Low Men as a monumental performance by Anton Yelchin and mentions that he was in New York the day before the shoot when Anton called him regarding a rewrite of the scene Scott had made with William Goldman. Anton told Scott he much preferred the earlier draft and felt he could play that much stronger. Scott adds that he trusted Anton's instinct, tore up the rewrite, went back to the original script, and this scene was the result.
The movie is clearly set in the summer of 1960, because Nixon has just been nominated for Republican candidate for Presidency. But when Bobby is reading the sports from the newspapers, he reads that Wills is going after Cobb's record. The year that Maury Wills challenged and eclipsed Ty Cobb's stolen base record was 1962.
When Bobby picks up the payphone, we hear a modern dial tone (at around 1h 21 mins). That tone was not introduced until the late-1960s, along with the introduction of touch-tone dialing.