As Yadav was speaking to the media, the unidentified man came up from behind and smeared his face with ink quickly and shouted “Bharat Mata ki Jai”.
Furious AAP activists caught hold of him and he was hit repeatedly before police intervened and led him away.
Yadav, the AAP candidate in the Lok Sabha election in Gurgaon in Haryana, was taken aback.
“I was talking to you when this person came from behind and put ink on my face,” he told journalists. “I did not see him.”
He added: “When you take on powerful forces in this country, one must be ready to pay a price. May God forgive this man (attacker).”