Hindu Yuva Vahini (HYV) is a Hindutva vigilante group, founded by Yogi Adityanath and "involved in many incidents of violence against Muslims". The group allegedly set ablaze two compartments of a train to protest Adityanath's arrest in the wake of violence in Gorakhpur in 2007. Sunil Singh, UP state president of HYV has 76 cases filed against him, of which 32 are for rioting.
Adityanath and HYV's strategy is to turn local confrontations between communities into cases of Hinduism under threat. For example, they escalated a dispute between a Hindu and a Muslim over who spat paan on whom into a full-blown communal confrontation in 2002. They played a similar role in the Mau riots of 2005. In October 2015, the group offered guns to Hindus close to where a Muslim man, Mohammed Ikhlaq, was murdered by Hindutva activists after his family were accused of storing beef.
References: Links to articles on Hindu Yuva Vahini on Narendra Modi Facts.