A 50-year-old man was stabbed in the arm during a fight on The Level, say Brighton Police.
Officers say they were called to the scene at about 8.15pm on August 5.
They said the victim declined to go to hospital but was treated at the scene by paramedics.
Officers said they used a Taser to detain a man at the scene.
Anyone who saw what happened or who may have information about the incident is asked to contact police online or by phoning 101, quoting serial 1430 of 05/08.
Alternatively they can contact the independent charity Crimestoppers anonymously, telephone 0800 555 111.
A 53-year-old man has been arrested on suspicion of causing grievous bodily harm.