Emergency teams saw a "rapid and sustained" fall in violent injuries during the first Covid lockdown, a study by Cardiff University has found.
However, there was no change in domestic violence admissions at Cardiff's emergency department.
The University Hospital of Wales said it saw the average weekly number of violent injury admissions drop from 28.4 pre-lockdown to 16.5.
There was also a 92% reduction in weapon use, according to the study.
Researchers from Cardiff University's Crime and Security Research Institute (CSRI) and the US Centers for Disease Control and Prevention studied data from Cardiff's only emergency department from March to June 2020 and compared it to weekly data from January 2019 onwards.
The findings - thought to be the first analysis of violence from this perspective during the Covid-19 pandemic - have been published in the Journal of the American Medical Association.
Lead author Professor Jonathan Shepherd, from the CSRI, said: "This sudden fall in violent injury is the largest any of us has ever seen.
"It's likely to reflect closure of city centre pubs and clubs in and around which most violence takes place, and widespread compliance with lockdown restrictions."
The team investigated the association between Covid-19 lockdown and emergency visits for violence-related injuries using detailed violence screening first implemented in Cardiff two decades ago.
They studied the time the violence took place, whether it was inside or outside the home, whether a weapon was used, the perpetrator type and the age and sex of the victim.
Prof Shepherd said there was no evidence of a significant change regarding violence in the home, which he said was "reassuring".
He said: "The massive decrease outside the home but no increase in the home reflects the nature of the two environments.
"The night-time economy - pubs and clubs and the streets where they are situated - is an environment which facilitates violence and violent injury.
"On the other hand, in our study, the home environment is much less conducive to violence and violent injury. People who would have been injured in violence in the night-time economy are not injured in violence when they stay at home."
Police in England and Wales had previously reported an increase in domestic violence during the lockdown from March 2020.
Cardiff University is due to release an England and Wales analysis of violence during the Covid-19 pandemic next month.