Did you notice that the wave in the foreground was headed offshore, away from the beach? The waves were reflecting strongly off the beach this evening. It made for pretty intense wave action as the crests from the incoming and outgoing waves collided.
When incoming and outgoing waves meet, the collision is called interference. When the crests combine, it is called "constructive interference" and the result can be a sudden, explosive increase in wave height. Some day I'll get a better picture of it, but here's one example: