In the UK if it leaves a mark. I think the Act was in 2004.
BB web site
"New smacking law comes into force
Parents in England and Wales who smack children so hard it leaves a mark will face up to five years in jail under new laws in force from Saturday.
Mild smacking is allowed under a "reasonable chastisement" defence against common assault.
But any punishment which causes visible bruising, grazes, scratches, minor swellings or cuts can face action.
The law is flawed and there should be a total ban on smacking, according to child protection charity the NSPCC.
It said the new law will only confuse parents and leave children still at risk of abuse.
It should be as wrong to hit a child as an adult
NSPCC boss Mary Marsh said: "There is a risk parents may choose to hit children on parts of their body where injury is less visible, such as the head, which can cause serious harm.
"Defining acceptable ways to hit children should become a thing of the past.
"It should be just as wrong to hit a child as it is to hit an adult." "