A Chinese man was detained after slapping a little boy hard across the face to teach him a lesson for beating his son and then entering a physical fight with the child’s grandfather who tried defending the boy.

The incident, which took place in the city of Nanjing, in the eastern Chinese province of Jiangsu, reportedly began after the toddler was caught fighting with his classmates in kindergarten over toys.

CCTV footage shows the moment the 33-year-old orthopaedic surgeon, named Mr Lu in local media, goes in to scold the kid who hit his son after learning of their fight.

But Mr Lu takes things a bit too far when the lecturing turns into him slapping the boy so hard that it knocks the kid off the plastic chair and onto the ground.

The boy’s grandfather, Mr Zu, 64, tries to reason with Mr Lu and gets in between him and the young boy, which quickly turns into an all-out row.

But neither of them backs down, and Mr Zu instead picks up the little plastic chair his grandson was sitting on and throws it in the grown man’s face.

A woman gets involved and attempts to intervene, but to no avail – as the elderly Mr Zu grabs a large wooden chair and tries to hit Mr Lu with it.

However, Mr Lu pushes back and shoves the old man onto the ground, reportedly breaking his leg.

At that point, the Nanjing police were called in to break up the fight and they ended up detaining Mr Lu and took the others in for questioning.

The case is currently under investigation.