Whilst jogging through Central Park, New York, the actor apparently confronted a group of boys who were attacking a stray dog.
According to a source at the scene, the Irish actor walked up to the three boys who were throwing rocks at the puppy - which they had cornered up against a bin.
'Liam yelled that they'd better stop or he'd knock the c*** out of them - but the punks just swaggered up and warned him to mind his own business.'
Liam then told the boys they better back off 'or else,' with them only eventually dropping their weapons when a policeman began to approach them.
The 61-year-old, who is used to playing hero characters in action films, then took it upon himself to comfort the frightened dog - stroking it whilst the policeman assessed it for injuries.
What a lovely man.