Constable Nicole Short received hospital treatment after attending a call in Kirkcaldy in May 2015 which resulted in the death of Sheku Bayoh.
A statement from her was published as part of a ruling by Lord Woolman who said the Scottish Police Authority (SPA) should re-consider applications from Ms Short and her colleague Alan Paton to retire on medical grounds.
Mr Bayoh, a 31-year-old father-of-two, died after being restrained by police officers using batons and incapacitant spray while responding to a call about a man with a knife.
Traces of alpha-PVP – an illegal substance also known as “flakka” which has been linked to bizarre behaviour – was found in his body after he died.
A Fatal Accident Inquiry or public inquiry is expected to be held if the Crown Office decides against criminal prosecutions.
In her sworn statement, which has not been tested by cross-examination, Ms Short, who has been on sick leave since the incident, said: “Mr Bayoh appeared to be on a mission from the manner in which he was walking. He appeared out of control and dangerous and given the reports of him chasing people with a knife as well as his demeanour and the way he didn’t react to the sprays, I felt that he could not be permitted to leave.
“I was terrified that he was going to kill a member of the public if he was allowed to leave the street, which is what he was trying to do.”
Ms Short said she did not see a knife, but believed Mr Bayoh had one on his person. She described him as being “like a zombie”. She said she felt “an enormous blow” to the back of the head and landed on the ground.
“I did not feel him hitting me again and I’m not sure that I was conscious, but I was later told that he stamped on me at least three times,” she said.
The SPA has so far deferred the applications for early retirement on health grounds arguing it would be against the public interest to allow them. But Lord Woolman said the SPA’s decision was “irrational”.
If the two police officers are allowed to retire, they would not be subject to misconduct proceedings.
Aamer Anwar, the lawyer for Mr Bayoh’s family, said: “Nicole Short talks of the fear of a murder taking place. The reality is that there was only one person that day who died – Sheku Bayoh. He was the only person whose body was covered from top to bottom in bruises, cuts and lacerations.”
David Kennedy, of the Scottish Police Federation, said: “We welcome the outcome of this judicial review which makes clear these officers suffered significant injury in the execution of their duties and qualify to retire on grounds of ill health. We hope that a decision is made soon by the Scottish Police Authority to allow this.”