Most read story: Waikato dad who viciously beat his nine-month-old son and only got home detention is now back behind bars

A father who viciously beat his nine-month-old son and avoided jail after being sentenced to nine months of home detention is back behind bars for an alleged pub breach.

This comes less than 48-hours after he was sentenced according to the NZ Herald.

The 20-year-old father, frustrated by the teething infant, beat his baby around his face and head, then jammed a solid object in his mouth causing part of his tongue to tear.

The Waikato man pleaded guilty on Monday at the Hamilton District Court on the attacks on his young son in February last year. 

Court documents reveal the nine month old was rushed to hospital with lacerations around his mouth, welts on both sides of his head, multiple cheekbone fractures, a torn bottom lip and tongue and facial grazes. 

His eyelids were so swollen that the baby could barely open them. 

The baby boys maternal grandfather told The NZ Herald that his family had been 'failed' by the court.

"If my daughter hadn't stopped him, he could have killed my grandson," he said.

"Home detention - this is a joke, a huge joke.

"There has been no justice for my grandson whatsoever. It's a slap on the hand, they might as well have given him a cup of tea and a big piece of cake as well."

Judge Denise Clark said she took into consideration the fathers remorse and promise of employment when sentencing him to home detention and 160 hours of community service.