If a player is injured while running to third base after a successful hit, can a batter waiting on deck serve as a courtesy runner?

The reason a player waiting on deck cannot serve as a courtesy runner for an injured player is based on the rule that specifies who is eligible to participate as a runner. Specifically, the regulations govern that only certain players can take on that role during a game. The rules focus on ensuring fairness and maintaining the integrity of the game, and that typically includes restrictions on who can actively play at any given time.

In this scenario, the batter on deck is still considered part of the upcoming batting order and thus is not classified as a non-base player. Moreover, this player is engaged in the game's current sequence and is not eligible to run for another player, as it would disrupt the established order of play and the workings of player substitution.

Other options incorrectly interpret the rules governing player substitutions and their eligibility to run. For example, the suggestion that any non-base player can serve as a runner overlooks the specific stipulations regarding the status of players at any moment in the game. It's important to refer directly to the relevant governing rules for the sport to clarify such situations effectively.