Amycus was already slightly off balance from having to tug the bottle out of Rodolphus' hand and he hit the ground hard when Rodolphus tackled him, his glass shattering on the floor.
He didn't have time to even try and block the punch that Rodolphus threw at him. His wand had flown out of his hand at the moment of impact and the only recourse left to him was punching Rodolphus. He couldn't get his arm free enough to hit him in the face so he punched him in the stomach instead. "Get off of me you tosser!" he shouted.