At 10.35pm on Monday, police were called to Lodge Terrace, in Beeston, where the 31-year-old man had been attacked with a bladed weapon.
He had puncture wounds to his back and shoulder and a laceration to his face.
The man was attacked by five men, after complaining about noise and anti-social behaviour from a group of youths in Trentham Park.
The suspects were described as black males, aged 18 to 20, and police are searching for the attackers.
The victim was taken to hospital but his injuries are not thought to be life-threatening.
Police cordoned off the park while they investigated the attack, but the cordon has since been removed.
Officers are patrolling the area as the Beeston community is left shocked by the incident.
Detective Inspector James Entwistle, of Leeds District CID, said: “This was a completely unprovoked attack on the victim after he complained about the group’s behaviour causing a disturbance in the area late at night.
“We are treating this incident very seriously and carrying out extensive enquiries to identify and arrest those responsible.
“We would like to hear from anyone who witnessed the incident or saw the group in the park and has any information that could assist in identifying them.
“We recognise that an incident of this nature will cause understandable concern in the community, and we are working closely with our colleagues on the local neighbourhood policing team who will be maintaining an increased presence in the area to reassure people.”
Anyone who witnessed the incident or who has any information that could assist the investigation is asked to contact Leeds District CID via 101 quoting crime reference 13220334115 or online via www.westyorkshire.police.uk/101livechat
Information can be given anonymously to the independent charity Crimestoppers on 0800 555 111.