A woman was stabbed in the leg trying to break up a fight between men at a tram stop.
British Transport Police (BTP) are appealing for witnesses after the woman was stabbed at Ampere Way tram stop last Thursday.
The 24-year-old woman, from Merton, had been out with friends and was waiting for a tram when the fight broke out at about 11.40pm.
The woman stepped in to calm down the altercation, but was then assaulted by members of the group. After falling to the floor she realised she had been stabbed in the thigh.
No weapon was found at the scene.
Detectives are appealing for witnesses and are keen to speak to a group of youths who are described as black and mixed race boys.
One youth in particular had distinctive hazel eyes.
Detective Sergeant Bob Stokoe said: "This attack left the victim requiring hospital treatment, not to mention causing her considerable shock and emotional distress.
"We are carrying out an extensive investigation into this attack, including making local enquiries and carrying out regular patrols in the area.
"We have also requested CCTV footage and are keen to speak with anyone who may have information key to our investigation."
Anyone with information is asked to contact British Transport Police on 0800 40 50 40 quoting B7/LSA of 2/09/2012, or Crimestoppers anonymously on 0800 555 111.