The incident took place yesterday when members of the Mohammadi Mission took out a march denouncing Kamlesh Tiwari's remarks and blocked the road at Balaganj crossing.
"Nearly 2,500 protesters blocked the road at Balaganj crossing though no permission was granted for the march," police said.
Police, initially, tried to persuade them to end their protest as action had already been taken against Tiwari, who has been booked and arrested under the National Security Act.
When they did not, baton-wielding policemen charged at them resulting in a clash as the protesters resorted to stone-pelting. Four policemen were injured in the violence, officials said.