Not recognizing his master, Jāmbavān challenged Him to fight. There was then a great fight between Kṛṣṇa and Jāmbavān, in which they fought like two opposing vultures. Whenever there is an eatable corpse the vultures fight heartily over the prey. Kṛṣṇa and Jāmbavān first of all fought with weapons, then with stones, then with big trees, then hand to hand, until at last they were hitting each other with their fists, their blows like the striking of thunderbolts. Each expected victory over the other, but the fighting continued for twenty-eight days, both in daytime and at night, without stopping.
Although Jāmbavān was the strongest living entity of that time, practically all the joints of his bodily limbs became slackened and his strength was reduced practically to nil, for he was struck constantly by the fists of Śrī Kṛṣṇa. Feeling very tired, with perspiration all over his body, Jāmbavān was astonished. Who was this opponent who was fighting so hard with him? Jāmbavān was quite aware of his own superhuman bodily strength, but when he felt tired from being struck by Kṛṣṇa, he could understand that Kṛṣṇa was no one else but his worshipable Lord, the Supreme Personality of Godhead. This incident has special significance for devotees. In the beginning, Jāmbavān could not understand Kṛṣṇa because his vision was obscured by material attachment. He was attached to his boy and to the greatly valuable Syamantaka jewel, which he did not want to spare for Kṛṣṇa. In fact, when Kṛṣṇa came there he was angry, thinking that Kṛṣṇa had come to take away the jewel. This is the material position: although one is very strong in body, that cannot help him understand Kṛṣṇa.
In a sporting attitude, Kṛṣṇa wanted to engage in a mock fight with His devotee. As we have experienced from the pages of Śrīmad-Bhāgavatam, the Supreme Personality of Godhead has all the propensities and instincts of a human being. Sometimes, in a sportive spirit, He wishes to fight to make a show of bodily strength, and when He so desires, He selects one of His suitable devotees to give Him that pleasure. Kṛṣṇa desired this pleasure of mock fighting with Jāmbavān. Although Jāmbavān was a devotee by nature, he did not know that his opponent was Kṛṣṇa while giving service to the Lord by his bodily strength. But as soon as Kṛṣṇa was pleased by the fighting, Jāmbavān immediately understood that his opponent was none other than the Supreme Lord Himself. The conclusion is that he could understand Kṛṣṇa by his service, for Kṛṣṇa is sometimes satisfied by fighting also.