According to students and teachers present there, the attacker called Kanhaiya for an interaction when he was attending the "nationalism" lecture at the varsity's administration block.
"Kanhaiya went to a corner to talk to him where the boy started abusing him and following the argument he slapped him. Seeing this, many students and univesity's security guards rushed to rescue him," a student said.
The varsity's security got into action and took the accused to the nearest police station where he has been detained for questioning, a police official said, adding his identity is yet to be verified.
Kanhaiya faces sedition charges in connection with an event on campus against the hanging of Parliament attack convict Afzal Guru during which anti-national slogans were allegedly raised.
He was granted interim bail for six months by the Delhi High Court last week after spending 18 days in jail. The students and teachers of the varsity had expressed apprehension about Kanhaiya's security after he was attacked by a group of lawyers in Patiala Court premises on February 17.
The Delhi police has asked the varsity authorities to intimate them about Kanhaiya's movements outside the campus. A man who claimed to be the president of "Purvanchal Sena" had last week announced a reward of Rs 11 lakh for anyone who shoots Kanhaiya. He was later arrested.