A girl of 12 was punched in the face by a scruffy, greasy-haired attacker.
She was walking past a greengrocers in London Road, St Leonards, when the man walked up to her and smashed his fist into her face.
The attacker then walked down the road to a cafe.
The victim was taken to the Conquest Hospital in Hastings after sustaining bruising to both eyes and her nose following Monday afternoon's assault.
Police officers said it was an appalling, unprovoked attack on a defenceless young girl as she minded her own business.
The attacker was white, about 6ft, of solid build, with shoulder-length wavy, greasy dirty hair, aged about 25 to 30.
He was unshaven and wearing a bright blue shirt, grey shorts and white trainers.
Anyone with information is urged to call PC Neil King of Hastings police on 0845 6070999 or Crimestoppers on 0800 555111.
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