It's the sound of the clapping that makes Ethan realize... they're not alone, and more than that, it makes him realize he's seconds away from throwing Damon overboard. As much as he may really, really want to at the moment, he knows Elena loves him and he is not going to potentially kill someone that she loves. He is also not quite ready to put him down either so Ethan just kind of grips hold of him there as his jaw locks, and he lifts up his fist to punch him in the face before he tosses him back on to the deck instead.

Where Damon lands unceremoniously.