My DM says that the wolf's bite attack causes a Str save or be knocked prone regardless of whether it hits or not.
The attack is:
Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 2) piercing damage. If the target is a creature, it must succeed on a DC 11 Strength saving throw or be knocked prone.
I thought it was implicit in the reading that the attack must first hit?