Ellie-Rose Hall, 14, was walking with her friend and boyfriend when she decided to run ahead and prank them by hiding in the bushes before jumping out.
However, she was shocked to discover a man already in the shrubbery.
The frightened teenager immediately leaped out, but the man followed her before she fell into a ditch.
Ellie-Rose then tried to get up but the man pushed her back down.
She was saved when her boyfriend spotted the commotion and shouted at the man, who then ran from the scene.
The attack left the youngster badly shaken up and her mother, Katie Hall, 32, was horrified to hear about what had happened.
The mum-of-four said: “She came in about 7.45pm on Tuesday night and she was petrified. It was horrible to see – absolutely dreadful.
“They pushed her to the floor and if her boyfriend hadn’t shouted at her a lot more would have happened.”
Miss Hall said her eldest daughter, who injured her ankle after falling over, barely slept on the night of the attack and has been really quiet.
The Kingswood Academy pupil also had the day off school and her mum fears it will trigger more panic attacks.
“I am worried about letting her outside but I don’t want to keep her indoors,” Miss Hall said.
“She has only recently started going out on her own because she is very panicky and suffers with panic attacks. Obviously this will set her back.
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“She has been really quiet and had hardly spoken to anyone. She is normally really bubbly and I can see it is affecting her.”
Immediately after her daughter returned home, the concerned mum reported the incident to the police.
She initially rang 999 before she was told to dial 101.
Miss Hall is now wary about letting her younger children go out and play in the block near her home in Amberley Close, off Dorchester Road.
However, she is keen to try and find the perpetrator hiding in the bushes who startled and ‘assaulted’ her daughter.
Miss Hall said: “I want to make sure people aware of what happened. People need to make sure that they are going out in groups.”
The incident happened shortly before 7pm on Tuesday night in bushes close to the distinctive red bridge which crosses Bude Road near the junction with Holwell Road.
Anyone with information which may help Humberside Police with their enquiries, should contact them on 101 quoting the crime reference number 16/45861/17.