Your coin was damaged with a pin hole on the surface of the coin. When the plating is split out, the zinc gets air. Then the breakdown process starts:

So that area is just damaged. But looking at the rest of the coin, this coin should have been discarded. Remember the rule about saving a coin:
If you would not buy that coin, why save it. Discard it un-looked at. Why waste your time on a disposable coin?