According to the ruling, what is the legality of sending a courtesy runner for a player before the first pitch is thrown?

Sending a courtesy runner for a player before the first pitch is thrown is considered legal under the rules. This situation acknowledges that teams may wish to replace a base runner in order to prevent injuries or manage player fatigue. The ability to send in a courtesy runner before the game begins allows teams to have the necessary adjustments for strategy without interrupting the flow of the game after it has started.

In this context, the ruling prioritizes player safety and the strategic elements of the game, ensuring that teams have the flexibility they need to field their players effectively.