Alex Martin swung a blow at his victim leaving the man lying on the pavement.
Gregor Purcell, prosecuting, told Lincoln Crown Court that Martin then kicked out two or three times at the victim’s head before he was pulled away by a passer-by.
Mr Purcell said “It does appear to be an unprovoked attack.”
Policed were called to the scene of the 4 am assault close to The Stonebow on Lincoln High Street and Martin was arrested.
Mr Purcell said: “He had to be restrained. He was very drunk. He spat at the police officer.”
The victim was left unconscious and was taken to where he was examined. Doctors found bleeding over an area of his brain and he was detained for 36 hours before being released.
Martin, 22, of Norton, Staffordshire, admitted a charge of assault occasioning actual bodily harm arising from the incident on January 30, this year.
David Eager, in mitigation, said that Martin has since been discharged from the Army as a direct result of the incident.
He said :“He served in Kandahar. He went out as a 19 year old boy and I suspect he saw things that no 19-year-old boy should see. He came back a different man.”
Mr Eager said that since leaving the Army Martin has found himself a job working as a labourer.
He said: “He has demonstrated genuine remorse. His life has already been blighted by his discharge from the Army.”
Martin was given a 12 month jail sentence suspended for two years with 210 hours of unpaid work.
Recorder Simon King told him: “It is shocking and disturbing that you should behave in that way. The assault was undoubtedly a serious one.
“Your victim ended up with what could have been a very serious injury indeed but I have been told there have been no long-term effects.
“You have been discharged from the armed services directly as a result of this offence and you are now having to make your own way in the civilian world. That in itself is some sort of punishment.”