At Goyle's insult, Heidi only gripped his collar tighter and growled.
Even with her quicker reaction time due to her quidditch skills, Heidi wasn't quick enough to fully dodge the punch and it his her cheek and she staggered back.
Quickly recovering though and ignoring the searing pain in her face, Heidi regained her momentum and grabbed onto Goyle's collar again and returned the punch with one of his own, straight to his nose, quickly followed by a second one. Heidi, even as calm and sweet as she usually was, was no stranger to fights. When she drank, she had a tendency towards more violent outbursts and had had her fair share of barfights.