Douglas Harper's Etymology Dictionary
Wiktionary
interleague
a. (context sports English) Between leagues; often specifically between the two major leagues of American baseball.
Usage examples of "interleague".
Baseball also tried expansion, interleague play, and radical realignment to bring the fans back, but it only slowed the slide.
I have this feeling that within a few months we're going to be reading about interleague lawsuits of galactic proportions.