Multiattack. The giant makes two greathammer attacks.
Greathammer. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit:28 (6d6 + 7) bludgeoning damage.
Rock. Ranged Weapon Attack: +11 to hit, range 60/240 ft., one target. Hit:29 (4d10 + 7) bludgeoning damage.