The earliest appearance of the word “jazz” (so far) is an obtuse 1912 reference to hokum in American West Coast baseball, nothing to do with music:

“I got a new curve this year," softly murmured Henderson yesterday, "and I'm goin' to pitch one or two of them tomorrow. I call it the Jazz ball because it wobbles and you simply can't do anything with it."[Jazz (word) wiki]

Note: Probably not a true “curve” but what the Yanks call a “knuckle ball” or “knuckler” today. Either way, erratic & unpredictable, ie: “cokey.”

Several more west coast popular sport references follow, all drawing on the “up tempo” usage of minstrelsy's “jasm” or “jasbo.”