A roofer headbutted and repeatedly punched a fellow drinker - knocking him unconscious - for trying to make him dance during a night out in Chelmsford.
Lloyd Kenlen, of Jarndyce, Chelmsford, was in the Golden Fleece in Duke Street when he attacked Daniel Maloney at around 2am on September 6.
The 26-year-old father of one pleaded guilty at Chelmsford Crown Court on Tuesday (October 28) to assault occasioning actual bodily harm and was jailed for nine months.
The court heard how Kenlen was drinking with friends after work when the Mr Maloney tugged on his arm to encourage him to dance.
The 26-year-old reacted by headbutting and punching his victim twice in the face, knocking him to the floor and leaving him unconscious for around 10 minutes.
Prosecutor Peter Clark said: "A witness said the first blow was a punch connected full in the face and the third and final blow was described as being 'a big left hook'.
"It was this last blow that perhaps caused the most amount of damage.
"The victim was knocked unconscious to the floor, was completely unresponsive and didn't seem to be breathing.
"When the ambulance arrived he was awake but seemed unaware of where he was and was confused."
'Mildly drunk'
The pub management cleared the building of customers so the emergency services could attend to the victim.
Mr Maloney was left with a black eye, bruising to his face, a swollen right cheek and thumb and was taken to hospital by ambulance.
After the attack the defendant tried to flee the pub, but after pushing past one member of security, was apprehended by door staff and held until the police arrived.
Lorna Glover, defending Kenlen said: "By the time of the assault the defendant was mildly drunk and was standing near the beer garden.
"Mr Maloney was dancing around and pulled on Mr Kenlen's arm in an apparent attempt to encourage him to dance.
"This behaviour angered Mr Kenlen in that moment and he assaulted him, that is not advanced as an example of provocation, Mr Kenlen wants to take responsibility for this offence, he apologises to the court and wants to be punished appropriately."
He has 33 previous convictions including threatening behaviour, common assault, theft, stealing a car and assaulting a police officer as well as serving a four-week stretch in a young offender institute in 2008.
Judge Anthony Goldstaub said: "For some reason you launched this unprovoked and unjustified attack. You headbutted him using you skull as a weapon.
"You are an athletic man and a strong man and you should not use those attributes to inflict harm.
"Your victim has a gap in his memory that you created by your unacceptable violence, at a time when people should be enjoying a peaceful evening."
The judge also ordered Kenlen to pay a £100 victim surcharge.
