A 59-year-old grandmother, who has a brain tumour, has been attacked in Milton Keynes after defending her 12-year-old grandson.
The boy had been near some shops in Conniburrow when he shouted at a man who he thought was dealing drugs.
The man chased the boy to his grandmother's home, which was nearby, and when she stood up to defend her grandson, the man punched her.
She was knocked to the ground and left shaken and upset.
The offender was described as black, aged between 25 and 35, 6ft (1.8m) and of muscular build. He was wearing a blue baseball cap, white T-shirt, grey tracksuit bottoms and white trainers.
The attack happened between 1130 and 1200 BST on 2 August, said police, who are appealing for information.
Det Con John Swallow, of Thames Valley Police, said: "This was a vicious attack on a vulnerable woman who was trying to defend her grandson."