The alleged assault followed an argument which broke out at the Four Seasons pub, Laindon, Essex, which eventually led staff to call police.
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The pub features a children’s play area, where the argument is reported to have begun, after one mother complained another parent’s children were uncontrolled and misbehaving.
The complainant was then surrounded by four or five people before the attack was launched. The victim reported a sore lump on her forehead just above the nose after the attack.
PC Marek Jaworski told the Liverpool Echo: "The victim, a 19-year-old woman who lives in Wickford, was in the pub from about 4.30pm with her children, playing and eating.
"After a couple of hours, there was a dispute.
"The problem was surrounding one of the parents not supervising their children while they were playing and their children were misbehaving.
"During the argument, about four or five people came over and this woman just remembers being hit in the face.
Pub staff intervene
"At that point the pub staff came over and tried to intervene.
"Someone at the pub called the police.
"The woman told police that she didn't know who these people were and had not met them before.
"There might have been quite a few people eating in that pub that evening who might have seen or overheard this altercation.
"It would have been relatively busy."
The attack, which is being treated as actual bodily harm, happened at about 7.30pm on May 15.
Last year the Good Pub Guide reported unruly children were the most common complaint from pub-goers.
Anyone with information can call Essex Police on 101, or Crimestoppers anonymously on 0800 555 111.