"There were two girls and another girl and they were yelling at her. She was huddled up in a corner and they were hunched over her - she was sort of cowering. It looked like they were being really aggressive.
"Having listened to Kerre and Mark right then, I thought, 'Now's my chance'. Kerre didn't have the chance to stop but I've got the chance.
"So I stopped, opened my car [door] and said, 'Leave her alone - what are you girls doing'."
The girls "panicked and bolted", he said.
The victim "picked up her bag, and looked at me, and then walked off". He estimated she was around 13 and seemed "pretty shy".
Nicholls said in the past he hadn't thought to stop.
"You don't want to get involved - their friends might be watching and you think someone might throw stuff at your car - it's easy to walk away.
"But with all the backlash, people saying to Kerre, 'You should have stopped' - I thought bugger it, I'll stop."
Nicholls has jumped in before, breaking up a fight in town and recently jumping over the fence to chase off burglars at his neighbour's house. But till now he'd never thought to step in to stop young bullies.
It was easy to dismiss bullies as "kids being kids ... they won't hurt each other - it's just a schoolyard thing and I won't get involved", Nicholls said.
As a dad and the family's sole income earner, he'd also become more reluctant to intervene than when he was younger.
"If they have weapons or something I would call the police and observe quietly but now if it's young kids I feel confident I can look after myself, jump in and help.
"It's a good feeling. She was probably too shocked to say thank you but I bet she was secretly stoked."
McIvor should "keep up the good fight", Nicholls said.
"Just because you didn't stop doesn't make you a bad person.
"We all have times we wished we had been the hero, but at least she followed up to do something about it."
