A 46-year-old man was left with a dislocated shoulder after an argument outside a pub in Hove.
The man was at the Slug and Lettuce pub, in George Street, when he became involved in a row.
Sussex Police said that it escalated and the man suffered the injury to his shoulder.
A 45-year-old man was arrested and questioned on suspicion of assault. He was later released on bail to return for further questioning on Thursday 25 July.
Detective Constable Leon Ryan, from Brighton and Hove CID, said: “Although a suspect has been arrested, we are still trying to establish exactly what happened to cause the injury.
“If you witnessed the incident, or heard the man shouting at passers-by prior to this, I’d like to hear from you.”
The row happened at about 6pm on Friday 28 June.
Anyone with information is asked to call Sussex Police on 101 or email email@example.com.