The man, identified as Sagar Bhandari, wearing trademark AAP cap and a badge, came from behind and smeared ink on Yadav's face when the AAP leader was talking to the media at the event organised to mark International Women's day.
After the incident, the attacker was thrashed by AAP volunteers following which he was taken away by police to Parliament Street police station. Later, he was taken to Ram Manohar Lohia hospital.
"I do not know who this person is. I was talking to media when I was attacked. This time they have attacked us from behind. Next time they will attack us from the front," Yadav said after the incident.
The AAP leader refused to lodge a police complaint into the incident and even visited the Parliament Street Police station to ask police not to register an FIR. His supporters were, however, insisting on doing so.
When asked whose hand could be behind the attack, Yadav said, "I could not see who this person was. I do not even know what his intention was. I do not want to blame anyone without verifying."
"I think when you step out in politics and raise your voice against bigger forces, then you should be ready to pay some prices. At least I am not ashamed of it," Yadav added.