Jeret Thomas Needham, 43, cried as Judge Leo Valentine Jr. pronounced his sentence.
Needham was convicted last month of second-degree murder in the death last Sept. 24 of Robert Colegrove.
Before he was sentenced, Needham told the judge that he was suffering from a concussion and wasn't in his right mind when he killed the 45-year-old victim.
Deputy District Attorney Michael MacNeil told jurors that the shooting was revenge-driven. The defendant's lawyer said his client fired in self- defense when he was threatened and saw the victim with a knife.
MacNeil said that about four to six months before the shooting, Needham had grabbed Colegrove's girlfriend's crotch as she bent over to make the bed in her boyfriend's room, a converted garage behind a home in Bay Park.
The day of the murder, Needham went to the home and got into a fight with Colegrove when the victim refused to get out of a chair, MacNeil said.
As Needham left, he walked by a woman in the home and repeatedly said, "Shouldn't have done that,'' according to the prosecutor. About an hour later, Needham came back and shot Colegrove once in the heart through a back fence, the prosecutor said.
Defense attorney Kerry Armstrong told the jury that Needham only shot Colegrove after hearing the victim say "I'm going to kill you'' and looking through the fence to see Colegrove holding a knife.
Armstrong said Needham met Colegrove through his girlfriend. He said that about eight months before the shooting, the defendant asked the victim if he wanted to help him coach wrestling at Madison High.
Colegrove worked as an assistant coach for only a week because he got hurt, Armstrong said.