There is not a lot of serious acting required in The Bad News Bears. Most of the real acting challenges fall on Walter Matthau in his role as Coach Buttermaker, as he is the only dynamic (changing) character in the film. Other stand-out actors in the film because of the size and nature of their roles are Tatum O'Neal as Amanda, Jackie Earle Haley as Kelly Leak, and Chris Barnes as Tanner Boyle, but none of them has to do anything particularly demanding. We are supposed to care about them to a certain degree, but the main focus of this movie is the baseball playing rather than character development. The only real noteworthy aspect of the acting in this film is the exchanges between Amanda and Buttermaker. Their conversations are very natural and do not feel very scripted, causing the audience to perceive them as real people and their relationship as genuine.

Because Hardball is more about people, the acting has to be even better than it is in The Bad News Bears. You have to believe that these are real people in real situations. Part of the time, this is accomplished through the actors having realistic reactions, such as Keanu Reeves' portrayal of Conor's emotional response and speech at G-Baby's funeral, Michael B. Jordan's portrayal of Jamal's when he is taken off the team because of an altered birth certificate, or Michael Perkins' portrayal of Kofi when his little brother G-Baby is shot. Never do any of these actors over-act, which would have made the audience at once accutely aware that they are watching a movie, nor do they play the scenes in a way that does not seem realistic, which could cause the same thing to happen. The best actors are always the ones who don't seem to be acting at all.

Equally important in acting can be a character's lack of reaction to an event. One shining example of this is near the middle of the movie when Conor walks one of his players, Andre, up to his apartment. Conor is astounded to walk past another apartment in which the whole family is sitting on the floor. He asks Andre why, and Andre, played wonderfully by Bryan Hearne, replies without any sense of emotion, "So they can stay below the windows." Conor asks why, and Andre replies matter-of-factly, "Bullets." His response is shocking exactly because he does not think it is unusual, and Hearne's delivery of the lines conveys this superbly.