You didn't often argue with anyone at the survey corps since there was no point, however you'd been quite frustrated with your own problems and it had been affecting your performance in battle. Your captain had picked up on it and soon pulled you aside to set you straight, however you snapped at him and took all your anger out on the man. Blaming him and his teaching to make him upset

You had walked away and immediately felt guilty...yelling at Levi like that.