The reverse of some 1920 Pilgrim Half Dollars developed a crack at some point, thus creating one of the more unusual varieties in the commemorative series. The crack appears between the mainmast (center of the coin) and the mizzenmast (the rearmost mast on the boat). It starts as a small, thin crack and eventually expands until it becomes a significant break (see illustration above). An interesting collection could be made by locating as many different die states as possible.
The rarity of this variety has yet to be determined, but it seems to be fairly common. PCGS has already certified over two dozen Mint State examples, including some unrecognized ones at the MS67+ level.