Under what cirstances can an officer tazer someone?

My boyfriend got into a fight with his mom, she called the police. Well, my boyfriend has a bad temper (not towards me) but he has ad/hd and when hes upset its almost impossible to calm him down. Basically they came and my boyfriend was real rude to the cop, screaming at him, calling him names, that sort of thing. After the officer told him to go to his car and my boyfriend said no, for what? than he told him he was under arrest and my boyfriend said why, this is stupid. im going back in the house. well when he turned to get up from a sitting position the cop tazered him, and he was arrested for resisting, ault on a peace officer, and some domestic charge. Since i was a witness i got sup. into court, and they asked me if i saw josh punch anyone, and i just told them what i saw. Well its getting sent to the grand jury, and when i talked to my boyfriend on the phone later he said he heard the officer say that josh had punched him. But i dont see where he would even have any marks? Another officer that wasn't even there is saying he saw him do it, and im really not sure what to do. Its basically my word and his moms against 2 sheriffs. We know josh was being an *** and deserved to get arrested, but not lied about. Would the officer lie to justify using a tazer? What do you think will happen?