Reports say Mr Kenny was waiting outside Birstall library in his car, after taking his wife there to return a book, when he saw the MP being verbally abused and attacked and got out of his car to help her.
As the assault began, it is believed Mr Kenny, who lives locally, grappled with the attacker and was stabbed in the abdomen by the gunman.
Police say his injuries are not life-threatening but he remains in hospital at Leeds General Infirmary.
A senior officer has praised his “brave” intervention.
Local sources said Mr Kenny is an ex-miner from Shawcross colliery in Dewsbury.
He later went on to join the Mines Rescue Service – elite teams of miners called in after accidents or disasters at Yorkshire coal mines.
One source said that Mr Kenny was involved in the pit rescue operation at Lofthouse colliery in 1973, when an inrush of water killed seven miners.
Neighbours told one national newspaper that Mr Kenny was a “great man” who “kept fit and can look after himself”.
“I was shocked, but I’m not surprised he did jump in to help. He’s a great guy, always happy to help out,” one neighbour is quoted as saying.
“He’s retired, but you wouldn’t think he was 77.
“He keeps active and swims every day. He’s quite private but we get on well.”
West Yorkshire Police’s temporary chief constable Dee Collins said: “During the course of the incident a 77 year old man bravely intervened to assist Jo and in doing so sustained a serious injury to his abdomen and although now stable he remains in hospital.”