The Bajrang Dal is the youth wing of the VHP, set up to mobilise youth for the Ayodhya movement. They can be regarded as a paramilitary wing of the Sangh Parivar whose role is to stoke communal tension and participate in communal violence (in Kishtwar, Warud and Muzaffarnagar for example). They played central role in the Gujarat pogroms of 2002.
Apart from communal violence, the Bajrang Dal and other organisations of the Sangh Parivar engage in "moral policing", often with the active participation of the police. This includes attacking young couples out together in public, or even having parties in private.
References:
• Articles tagged with Bajrang Dal on The Wire, kafila, Communalism Watch and Narendra Modi Facts.
• Bajrang Dal on Wikipedia.