Nathan Bigby clashed with Joshua Kirkham after spotting him holding the woman's coat and looking for her outside The Stourbridge Lion in the town's High Street which the victim had just left at 3am on July 27, a judge was told.
He had talked to her in the pub because he knew her from school and was having a good time, Mr Stuart Clarkson, prosecuting told Wolverhampton Crown Court.
Bigby walked up to him and declared: "That's my girl. Don't talk to her. You don't know who I am," continued the prosecutor who added: "After that he appeared to calm down for a short time until, for no apparent reason, he punched him in the face, knocking him down.
"The victim was semi conscious on his back and the defendant continued to punch him before moving away and was restrained others when he tried to attack him again." The defendant was arrested later at a McDonald's restaurant and claimed the other man had touched the backside of the woman who did not support the prosecution case.
Mr Kirkham suffered a fracture skull together with two nasal bone fractures and was detained in hospital for four days. He said the attack had significantly affect his social life because he did not feel safe going out anymore.
Ms Caroline Harris, representing Bigby, said the incident was "out of character" for the father of one whose work was praised in a letter to the court from the man he has worked for over the past eight years. The lawyer added: "The complainant did not turn up for further medical appointments and so, presumably, has made a good recovery."
Bigby from Halesowen Road, Dudley admitted causing grievous bodily harm with intent and was sent to prison by Judge Jinder Singh Boora who told him: "Nothing in your history would suggest you would behave like this. You are not a bad person by nature but circumstances can make you bad. This was a sustained and repeated assault during which you rained down blows as he lay face up and was unconscious for a time. He looked a complete mess."