When is courtesy runner legally in game?

[RKBUmp]

I believe it is going to depend on which rule set you were playing under. ASA doesnt mention it under courtesy runners other than they must be reported to the plate umpire, but under substitutions once reported to the plate umpire they are considered in the game.

As I recall, FED this year came out with a ruling that substitutes were not officially in the game until a pitch had been thrown.