Raised a Catholic, Neeson told Men’s Journal he was 9 years old when his parish priest offered to teach him how to box.

He Was Once A Champion Boxer

The “sweet science” came naturally to him, and Neeson discovered he possessed a strong left jab. He went on to become a champion fighter in three different weight divisions.
Liam Neeson on "Kinsey" - CBS News

Despite his success in the ring, Neeson disliked the potential for abrasions and fractures, both to himself and any opponents he might face. He won his final match about seven years later, but decided not to continue boxing due to a concussion he had sustained during that fight.

Liam Neeson übernimmt Hauptrolle bei "Die nackte Kanone"-Reboot | WEB.DE

All his pugilistic experience came in handy later, when he portrayed a boxer in the 1990 film The Big Man: Crossing the Line.