Looks like the antler snapped off with a clean break. He probably rubbed it against a palm tree. The bucks can cause destruction to the trees at this time as they spar with the branches to get the antler off and sometimes the entire tree is knocked down.
The people in the neighborhood must not be feeding this deer very much as is evident by his protruding ribs. These are the first two bucks I have seen this season with their antlers already shed.
