The evidence comes from a discussion of the Creek Indians (Muscogee Confederacy) by Albert James Pickett, History of Alabama, Chapter 3, "The Modern Indians of Alabama, Georgia and Mississippi," 1851, available online at https://web.archive.org/web/20020613101037/http://homepages.rootsweb.com/~cmamcrk4/pkt3.html (for other chapters, see the title page and contents):

Their most manly and important game was the "ball play." It was the most exciting and interesting game imaginable, and was the admiration of all the curious and learned travellers who witnessed it. The warriors of one town challenged those of another, and they agreed to meet at one town, or the other, as may have been decided. For several days previous to the time, those who intended to engage in the amusement took medicine, as though they were going to war. The night immediately preceeding was spent in dancing and other ceremonious preparations. On the morning of the play, they painted and decorated themselves. In the meantime, the news had spread abroad in the neighboring towns, which had collected, at the place designated, an immense concourse of men, women, and children -- the young and the gay -- the old and the grave -- together with hundreds of ponies, Indian merchandise, extra wearing apparel, and various articles brought there to stake upon the result.

The players were all nearly naked, wearing only a piece of cloth called "flap." They advanced towards the immense plain upon which they were presently to exhibit astonishing feats of strength and agility. From eighty to a hundred men were usually on a side. They now approached each other, and were first seen at the distance of a quarter of a mile apart, but their war songs and yells had previously been heard. Intense excitement and anxiety were depicted upon the countenance of the immense throng of spectators. Presently the parties appeared in full trot, as if about to encounter fiercely in fight. They met and soon became intermingled together, dancing and stamping, while a dreadful artillery of noise and shouts went up and rent the air. An awful silence then succeeded. The players retired from each other, and fell back one hundred and fifty yards from the centre. Thus they were three hundred yards apart. In the centre were erected two poles, between which the ball must pass to count one. Every warrior was provided with two rackets or hurls, of singular construction, resembling a ladle or hoop-net with handles nearly three feet long. The handle was of wood, and the netting of the thongs of raw hide or the tendons of an animal. The play was commenced by a ball, covered with buckskin, being thrown in the air. The players rushed together with a mighty shock, and he who caught the ball between his two rackets, ran off with it and hurled it again in the air, endeavoring to throw it between the poles in the direction of the town to which he belonged. They seized hold of each other's limbs and hair, tumbled each other over, first trampled upon those that were down, and did everything to obtain the ball, and afterwards to make him who had it, drop it before he could make a successful throw. The game was usually from twelve to twenty. It was kept up for hours, and during the time the players used the greatest exertions, exhibited the most infatuated devotion to their side, were often severely hurt, and sometimes killed, in the rough and unfeeling scramble which prevailed. It sometimes happened that the inhabitants of a town gamed away all their ponies, jewelry and wearing apparel, even stripping themselves upon the issue of the ball play. In the meantime, the women were constantly on the alert with vessels and gourds filled with water, watching every opportunity to supply the players.

[This passage apparently cites or quotes "Narrative of a Mission to the Creek Nation," by Col. Marinus Willett, pp. 108-110, in Bartram's Travels, pp. 482-506.]