Police say the apparently deliberate act happened when a woman pushed a car door into the victim’s back as she was seating her child inside.
The incident happened at about 3.30pm on Monday, March 20, in French Drive.
The two vehicles involved are described as a black saloon car and a silver people carrier.
The offender is described as white with a large build, about 30-years-old, about 5ft 5in with brunette hair tied in a ponytail and dark, oval-framed glasses.
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Witnesses can contact police on 101 or Crimestoppers anonymously on 0800 555111.