We have no idea what happened so cant really comment.
But let's paint one scenario (I have made this up and it has no basis on fact).
His teenage kids are going to a party and he tells them to be back by 11pm.
He phones them at 11pm and they refuse to come back.
He says if they are not back by 11:30pm he will lock them out.
They arrive home at say 11:45pm, perhaps a little drunk, finding the front door locked and they cant get in.
They start shouting to wake their parents up, and maybe when that fails they start shouting abuse at their parents.
No luck so they start throwing stones at the window. Being a bit drunk one of them throws a brick and it smashes a large front window on the house.
Father wakes up and goes down stairs, and being very annoyed, gives them both a clip round the ear.
I may be totally wrong, but which parent would say they would not clip their children round the ear in that situation.