It was alter post strike. On another coin that looked similar to this one, you can see the reverse die was in really bad shape:
But notice one thing that doesn't look like the die issue? Note the rim. The rim is normal. That tells me it is a die issue, and not an altered coin. On this coin (OP's) note the the rim is also affected. So this tells me it is not a die issue (die event). But an alteration of the coin.