Police have registered an FIR against Rashtriya Janata Dal MLA Sanjay Kumar Singh Yadav for allegedly abusing and assaulting a government school headmaster in Bihar's Rohtas. In a separate police complaint, Yadav has also been accused of threatening 14 other school teachers for their alleged failure in providing two buses for RJD chief Lalu Prasad Yadav's rally in Patna.