What dictates that a team must have a designated hitter or opt for no DH for a specific game?

The designated hitter (DH) rule in baseball allows teams to decide whether to use a DH in a game. This decision is formalized when the team submits their lineup card prior to the game. By including or excluding a DH in the lineup card, the team establishes its choice regarding the use of the DH for that specific game, which then sets the rules for player substitutions and batting order.

This process ensures that both teams are aware of each other's strategies and lineups before the game begins. The decision is binding for the duration of the game once the lineup is submitted, making it crucial for teams to finalize their intentions regarding the DH before play begins. Therefore, the requirement to submit a lineup card is what dictates whether a team will have a designated hitter or not in a specific game.