A nurse from Brighton suffered a serious injury to her eye while the March for England and counter-protest were taking place last weekend.
The 25-year-old woman was an innocent passer-by when a thug threw a missile which hit her in the face.
Sussex Police said: “She crouched to the ground with blood coming from her left eye.”
The force said that she had not been taking part in the march or protest but had arranged to meet a friend on the seafront.
She was heading towards the Palace Pier at about 1pm when the thug struck.
Sussex Police said that she was “thought to have been the innocent victim of an attempted assault on participants in the March for England event”.
She was trying to leave the car parking area in the front of the Royal Albion Hotel but she was unable to continue because of the large crowds.
She was standing near two men thought to have been participants in the march when something hit her in the face.
Several people went to her aid and she was taken to a nearby ambulance for treatment before being taken to the Sussex Eye Hospital in Brighton by a paramedic car.
Sussex Police said: “At this stage permanent damage to her eye has not been ruled out.”
Detective Chief Inspector Carwyn Hughes, who is leading the investigations into a number of offences alleged to have occurred during the event, said: “It would appear that this lady has been very unfortunate in having coincidentally been close to two men who seem to have been the targets of the missile thrower.
“She recalls that both the men were shaven-headed and had heavily tattooed arms.
“There were a number of minor injuries caused by missile throwers on the day but this is far more serious and we would like to speak to anyone who witnessed the incident, especially any of the people who went to the woman’s aid or who may have been in the vicinity of the missile thrower.”
Anyone with information is asked to call Sussex Police on 101 or the independent charity Crimestoppers anonymously on 0800 555111.
Twenty people were arrested last Sunday (21 April) for offences believed to have been related to the march and protest.