He grabbed one bull by its horns, resulting in him being gored and suffering a serious injury.
Police then had to shoot both bulls.
Police told WMUR that the attack and the deaths of the bulls were preventable.
"I think it's very tragic," Sergeant Daniel Wicks of the Brentwood Police Department said.
"I just saw the farmer. He's very upset about it, and it was probably avoidable if the person had avoided the bull and did was he had been told to do."
The man who was gored, John Fabiano, disputed the police version of events.
"Nobody spoke to me at all," Fabiano told local news outlet Union Leader, adding that he "never talked to anybody".
He claims he was chased by one of the bulls before deciding to take action.
"The bull looked me right in the eyes, like with his left eye, and from there I knew what he was going to do," Fabiano said.
He told the Union leader: "The reaction time was like zero - either do it now or get seriously hurt or even die."
After grabbing the horns he was flipped, landing on the horns of the other bull.
From his hospital bed, Fabiano said he doesn't feel lucky "because I'm in serious pain".
