Sentence:  Theon Greyjoy is the most well developed character on that stage, and the action comes down to him. Euron, with Yara underneath his ax, goads Theon into attack. But Theon is overwhelmed by the violence all around him, and instead he jumps <WSD>overboard</WSD>. 
Meaning of the word marked with <WSD> tags:  Over the edge; especially, off or outside of a boat.