A Strathfield 71-year-old grandmother is fighting for her life after allegedly being punched in the head in a Sydney park - which left her grandson horrified.

Police allege a 52-year-old man named by 9News as John Bozic attacked the elderly woman in a park on Francis Street, Strathfield on Thursday.

Around 12:10pm on Thursday, emergency services were called after reports the woman had been punched in the head by a man who fled the scene.

The grandmother had been at the park with her six-year-old grandson.

Police will allege a dog belonging to Mr Bozic took a ball from the boy.

Channel 9 reports the grandmother then raised her concern with Mr Bozic, and after that called her son-in-law to the scene.

Moments later, the 52-year-old allegedly punched the woman, leaving her critically inj

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