Shocking video footage has been shown in a Wollongong court of an intoxicated father leaving his nine-month-old son unattended to chase after his mate and knock him unconscious.

The man, who cannot be named, left the child unrestrained in a pram precariously close to stairs at Thirroul railway station on the evening of December 27, 2014, to run after the victim following an argument between the pair.

The footage shows the father throw a series of punches at his friend, the second of which appears to knock the man out cold, causing him to slump to the ground.

The father goes back to his son, but then returns to his unconscious friend's side when another man arrives.