When Rabastan took the bottle again and glanced around his brother made a face. It was his attempt to tell him he did not have to drink more without actually saying it. Rodolphus was not one to cross the crowd but this was his little brother. He could not just tell him don't do it but at the same time he really could not stand there and watch it happen, but in the end that was all he could do.
It was the moment that Rabastan finished the swig he took that made Rodolphus want to grab him and pull him away from the pitch. He was so torn between his loyalty to his little brother and the team. That and what would happen should he cross Lucius and take Rabastan back to the common room, or even better his own room. Rodolphus actually felt completely and utterly powerless at that moment.