Bad guys in movies learn quickly not to mess with Liam Neeson. So do people who take him on in real life. According to Neeson’s interview on Highly Questionable, in the mid-1970s, he was in training to become a teacher.

He Reportedly Punched A Teenager Who Threatened Him

One day, he attempted to get his rowdy students to settle down to begin his lesson.
Liam Neeson - News - IMDb

A sizeable 15-year-old boy refused to listen, continuing to be disruptive. Neeson told him to leave the classroom, at which point the kid took out a blade.

Liam Neeson : Awards | Carnegie Corporation of New York

Neeson responded by allegedly punching the student, though he later admitted in the interview that his actions were wrong. The school administration reprimanded Neeson, and he resigned a short time later.

Liam Neeson: Release date announced for Naked Gun remake starring Ballymena  actor | BelfastTelegraph.co.uk