MLB Slam! is an MLB-licensed baseball game that offers six game modes. It uses the MLB statistics of the 2003 season based on the league standings as of 26th August of that year and all 30 teams. In Quick Match a quick game can be played with randomly assigned teams. Spring Training is similar, but there the teams can be chosen. Full Season is the main game mode with a season 162 games. It follows the 2003 schedule and includes all inter-league games and the World Series. A season is started with an opening day MLB roster or a dream team. A dream team can be used in all games modes except for exhibition games. A dream team is built starting with a $45,000 budget for a 15-person roster including at least three pitchers and one player for each position. Players can still be bought or sold afterwards and money is earned based on the performance. During a season statistics change based on the performance. Games can be simulated to move quicker and tactics include setting the batting order and field lineup.

The three remaining game modes are World Series, Homerun Derby and 2 Player Game. World Series takes a team immediately to the World Series for the conclusion without having to play an entire season. Homerun Derby is a game of three rounds where two team take turns hitting the ball out of the park. After ten outs the teams switch positions. 2 Player Game is a local competitive multiplayer game using Bluetooth. There are three difficulty levels.

As in most baseball titles a game is split up into different phases, each with their own controls for hitting, running, pitching and fielding. However, outfield and base running are left almost entirely under the control of the computer. Hitting a ball is done by moving a target into a strike zone where the pitch will cross the plate while simultaneously timing the swing button. While pitching a small selection of pitches is offered, along with moving a target in the strike zone and timing a power meter to determine the speed.