Police were today hunting two vehicles which failed to stop after hitting a man.
It is thought that the victim, who was fatally injured, had earlier been assaulted.
Scotland Yard said officers were called at about 11.40pm yesterday to reports of a traffic incident at the junction of Trinity Road and Magdalen Road in Wandsworth, south west London.
The 40-year-old man was taken to a south London hospital, where he was pronounced dead at 1:53am.
A spokesman said it was thought that the man's identity was known, but formal identification was awaited. Next of kin have been informed.
A post mortem examination will be held in due course.
"At this early stage, it is believed that the man was the victim of an assault prior to being in collision with two vehicles that failed to stop at the scene," the spokesman said.
"A 25-year-old man has been arrested on suspicion of assault and is in custody at a south London police station."