(Hanuman, who aided Lord Rama, during the time of Krishna positioned himself atop the chariot to help His devotee, Arjuna win the war)

Arjuna prayed to Anjaneya to fight on his side at Kurushetra; but Anjaneya said that the Kaurava army would be too infinitesimal a foe for his prowess; it would not be fair to pit him against such a weak enemy; he would only watch the fight, from the flag of Arjuna’s chariot, he said, and the offer was gladly accepted. (SSS Vol.4, p. 58)