Robert Hart, who attended Manchester’s Heaton Park event in June of that year, had an argument with another man after a blow up-doll in the crowd hit his girlfriend Gemma.
Gemma said she fell to the ground and Robert confronted the person over the incident.
The boyfriend was punched in the head and died in hospital five day later.
“There was an inflatable doll. It got chucked over once then chucked back over. The second time, it hit me and covered me in mud,” Gemma told BBC’s Crimewatch show.
“And that’s when Rob turned around. He actually said he didn’t want any trouble. And that’s when they have turned into a scuffle.
“I was trying to get Rob away and that’s when I got knocked over. And then it was only within seconds that he came down next to me.
“Someone just said to me ‘we have got him back’. The next thing I knew he was just apologising to me. He was dazed, you know. You think because people are telling you he is alright, he is alright. He was far from it really.”
Robert, from Macclesfield, was a big Manchester City fan who loved playing the guitar, his girlfriend said.
Since March of this year, Police has offered a £50,000 reward to anyone who finds the person responsible for Robert’s death.
The perpetrator has been described as ‘mixed race, in his mid-20s, around 6ft to 6ft 2in tall, of muscular build with short, dark hair which was shaved at the sides’.
Detective Inspector Madeline Kelly, from GMP’s Major Crime Review Team, said: “Even though this terrible incident was almost 10 years ago, it will still be fresh in the minds of many people, especially Robert’s family and people who were at Parklife.
“Despite the passing of time, the heartache felt by Robert’s family has not faded.
“Just as we were in 2014, we are determined to catch the person responsible which is why we are taking a fresh look at the evidence and appealing for the assistance of the public.
“We are appealing for people to dig deep into their consciences – it you were one of the people involved on the day we would urge you to come forward.
“No-one went to the festival that weekend with thoughts of violence.
“Allegiances and friendships will have changed so if anyone has any information they can report it to police in confidence, particularly if they feel they could not before.
“We are also asking for people at Parklife on Saturday 7 June 2014 to share their photos and videos with us – especially people who were around the main stage at around 9pm just after Rudimental had finished their set and before Snoop Dogg was due on.”