The former Mad Men star portrays a teacher with a dark personality in the movie, and one scene required her to show off her secret knife skills to a fellow staff member, as played by Ice Cube.

Christina expected to pull off the move with a small folding blade, but she was left panicking when she realised the prop producers actually had in mind was a lot bigger than she had imagined.

"I had bruised fingers because I knew I was supposed to have a knife, but I thought it'd be a switchblade," she explained on U.S. breakfast show Today. "And they (producers) were like, 'It's a butterfly knife', and I was like, 'I don't know how to do that!' So I sat there in my trailer hour after hour and (practised before filming)."

Despite playing a strong character onscreen, Christina admits she was a little nervous the first time she met rapper/actor Ice Cube, although she soon learned he was a softie at heart.

"He's a bada**!" she laughed. "I will not lie that I was very intimated when he walked in the room and he has this very strong presence and everyone just pays respect, but he's super nice and sweet and welcoming and cool."

Fist Fight also features comedian Tracy Morgan in his first film project following a near-fatal traffic accident in 2014, and Christina reveals her castmates all revelled in hanging out with the funnyman in between takes.

"We had a lot of fun...," she shared. "We'd hang out in the music room and the gym in between (scenes) and just listen to Tracy Morgan being hilarious. We didn't want to miss a moment so we just all hung out together. It was nice."