A policeman was injured seriously when some miscreants stabbed him after he questioned them for smoking in public in the city on Saturday.
Head constable Nagaraj has been admitted to hospital, police said.
"He asked some men why they were sitting and smoking, when suddenly one of them took out a knife and stabbed him.
They pushed a constable who was with him and fled the spot," DCP (North Bengaluru) N Shashi Kumar told reporters.
The two policemen had gone to the spot after a complaint was received from residents that some miscreants camp in their locality and create nuisance.
Police have launched a manhunt for the assailants.