When Arvind Kejriwal was shaking hands with supporters, the person punched the AAP chief on his back and then slapped him.
Later the man was thrashed by AAP workers and handed over to police.
"Some people are ready to go to any extent to become Prime Minister. Let them do whatever they are doing. Our religion teaches us non-violence. If we raise our hands, this movement will come to an end," Arvind Kejriwal said.
Appealing for calm, the AAP leader asked his supporters not to indulge in any violence.
Arvind Kejriwal has been attacked a number of times in the past.
On March 28, he was attacked by a man, who claimed to be a supporter of anti-corruption crusader Anna Hazare, during his election rally in Haryana.