What occurs when the defense appeals that a runner on second base left early on a caught fly ball?

When the defense appeals that a runner on second base left early on a caught fly ball, the outcome is that the runner is declared out. In baseball, once a fly ball is caught, runners are required to tag up—meaning they must remain on their base until the ball is caught before attempting to advance. If the defense notices that the runner left the base before the catch was made and successfully makes a legal appeal, the umpire will rule that the runner on second base is out for leaving early. This is an important aspect of the game's rules, as it emphasizes the importance of correctly adhering to tagging up on fly balls to ensure fair play.

The other choices do not align with the rules governing this situation. The runner cannot be declared safe, as the appeal process directly addresses the infraction of leaving early. An appeal is valid when made properly, challenging the action of the runner. The notion that both runs score is incorrect, as the out negates the advancement of that specific runner.