What happens if a designated hitter goes on defense?

When a designated hitter goes on defense, the role of the designated hitter is terminated for that game. In baseball, the designated hitter rule allows a player to bat in place of the pitcher to enhance offensive performance without requiring the pitcher's batting. However, the moment the designated hitter takes a position in the field, the team must revert to the traditional rules where all players must bat for themselves. Therefore, the designated hitter's role ends, and that player must now follow the rules as a regular fielder.

This is an essential aspect of the game that ensures clarity in player responsibilities and maintains the integrity of the designated hitter rule. The other options don't align with official rules regarding the designated hitter; for example, the designated hitter isn't allowed to continue batting for another player once they enter a defensive position, nor can they play defense only due to injury. Also, terminating the DH role does not result in a forfeit of the game.