What happens when an unreported substitute bats in place of a designated hitter without notifying the umpire?

When an unreported substitute bats in place of a designated hitter without notifying the umpire, the correct outcome is that the umpire will make necessary lineup changes upon discovering the substitute. This aligns with the rules that govern substitutions in baseball, emphasizing the importance of proper notification to the umpire regarding player changes.

In the case of an unreported substitute, the play remains valid until the substitution is recognized and addressed. The umpire must then correct the scorebook according to the actual players who participated in the play. This ensures that the game maintains accurate records of player participation and upholds the integrity of the rules.

The other choices do not accurately reflect the established procedures in baseball for handling situations involving substitutions. The plate umpire being able to record an intended substitute does not align with the rule's intent, as effective communication about any substitutions is essential. Moreover, the discussion of an out being declared or consequences faced by the opposing coach does not properly capture the procedure for rectifying such mistakes, which focuses more on correcting the official lineup than penalizing either team.