A refuse collector who attacked a Booths supervisor at the Barrowford store alleged the victim had been "harassing" his partner, a court heard.
Damian Gray (29) hit Shaun Benson, who was on his break and talking to a female colleague outside at the time. Mr Benson ended up with blood on his clothes and there was also blood on the ground after the violence on February 4th, Burnley magistrates were told.
Mr Benson, who suffered a forehead injury, told police the defendant had gone up to him, made comments about speaking to other people's girlfriends and "swung" for him.
Mrs Alex Mann (prosecuting) told the hearing: "It was a relatively severe injury for common assault."
Gray, who has never been in trouble before, had at first been asked to pay Mr Benson £100 compensation, but had not handed the cash over.
The defendant, who was not represented by a solicitor, told the court: "I would just like to say I'm very sorry. It was totally out of character. I know it was completely unacceptable. I haven't just got up and assaulted him. Regardless of that, what I have done is unacceptable and it won't happen again."
Gray claimed the victim had been harassing his partner, who had also worked at Booths, for some time. The store said it would keep them apart, but it carried on.
The defendant added: "I had gone to see my partner on my break. She told me it had carried on. I was on the car park. She got out of the car. He's come out of the door and, wrongly, I stopped and wound the window down. I got out of my car and stood at the door, arguing with him.
"He called my partner a liar. I saw red. As soon as I saw I hurt him, I left the situation. As a result of these events, my partner left the job. That caused financial difficulties and strain at home."
Gray, of Newfield Drive, Nelson, admitted assault by beating. He was fined £83 and must pay £100 compensation and a £30 victim surcharge.