I'd actually say it's a retained cud because you can see the rim is still visible. So the piece of the die is still present but has been severely vertically displaced. If it was completely gone and this was a full cud, there would be no evidence of the rim in that location. On the obverse side you'll notice a weakness in the rim and the base of the three in the date. This is due to a lack of pressure caused by the displaced piece of the die on the other side.