The plains Indians knew how to fight, and much better than this. Man for man, they were better than our cavalry. There just were not very many of them, and they did not have our logistics support. That doomed them. Eventually, all the smart one signed treaties or surrendered. There are probably more Indian genes in America today than there were in 1870. My kids have some of them.
Well, they knew how to fight the way THEY were accustomed to fighting. But their way of fighting was more like a game than war.
When they really wanted to put one over on the enemy, they did it sneakily, at night, slitting throats and stealing horses.
When they went "visible" it was no more "war" than a teens' game of "Capture the Flag."
FWIW, this myth that they were a "great horse cavalry" is baloney.