Contractor Vikas Kumar Jha accompanied by his cousin and two others entered the chamber of Chief Engineer Narayan Paswan and assaulted him, Deputy Superintendent of Police, Sachivalya, Shibli Nomani told PTI.
The office staff came to Paswan's rescue and informed the police.
A team of police arrived and arrested the four on complaint of the victim Engineer, Officer in charge of the police station Ramesh Kumar said.
The complainant said the contractor was angry with him due to rejection of his tender for installation of handpumps.