Yes, there is the concept of selective inforcement. Do you slam water smugglers? Or do you maintain order while watching water pass by? I know lots of police who inforce the law but aren't going to jump a poor man's pick up truck over a crack in the windshield. They wouldn't bust an old man carrying water either. It is also called common sense.
I think that, given that their instructions are to prevent people from crossing the police barricade, preventing somebody from crossing the police barricade is probably "maintaining order".