"Could you please organise another win for us?" magistrate Elizabeth Ellis asked Kenny in Wyong Local Court on Thursday.
Ms Ellis told Kenny she was effectively giving him a caution for headbutting his victim.
She said Kenny could honestly say he had not been convicted of a criminal offence if he stayed out of trouble for the next 12 months.
Outside court, Kenny, 61, the Parramatta Eels great and NRL Hall of Fame inductee, said he was happy with the result.
He had pleaded guilty to the assault and was placed on a 12-month conditional release order without conviction.
The agreed statement of facts revealed Kenny had met the victim, Scott McMonigal, 58, once or twice over the past 10 years.
Kenny had been in a previous relationship with Mr McMonigal's girlfriend, Karen Ross, who worked at the Police and Community Youth Club at Bateau Bay on the NSW Central Coast.
Police said Kenny was driving in to the PCYC at 2.30pm to go to the toilet and play basketball with some children as Mr McMonigal was driving out on April 12.
Ms Ross told Kenny: "He has obviously seen you come in."
Kenny replied: "Karen, we have done nothing wrong."
Kenny returned to the PCYC at 5.30pm for his regular training session when he saw Ms Ross who was still upset Mr McMonigal had seen Kenny.
"The accused (Kenny) remained with the witness (Ms Ross) who informed him of issues and incidents in her current relationship with the victim (Mr McMonigal)," the statement of facts said.
"The accused was doing his best to console the witness."
Kenny, who did not know Mr McMonigal had returned to the PCYC, grabbed his belongings from the reception area and was heading up to his training session when he saw Mr McMonigal talking to Ms Ross.
Kenny walked up to Mr McMonigal and said "get out of my way", before they were facing each other only 2cm to 3cm apart.
Kenny told Mr McMonigal "if I hear you lay a hand on her, I'll make sure you don't do it again", before headbutting him.
Ms Ross asked Kenny to leave and when he refused, she called the police.
Mr McMonigal then went to The Entrance police station to report the incident and took out an apprehended violence order against Kenny.
Mr McMonigal claimed he feared for his safety, Kenny's behaviour towards him had been "ongoing for some time" and he was capable of committing further offences.
Kenny was later arrested at his Shelly Beach home and charged.
The incident came almost a year after Kenny consented, without any admissions, to an AVO taken out against him by police on behalf of his estranged second wife Suzanne.
Kenny, who was diagnosed with Non-Hodgkin lymphoma cancer in 2017 but is now in remission, played 17 Tests for Australia, 17 State of Origin games for NSW and won four premierships with Parramatta in 1981, 1982, 1983 and 1986.
His son, Mitch, 24, plays for Penrith as a hooker.
1800 RESPECT (1800 737 732)
Lifeline 13 11 14
