Wiktionary
leaguist
a. Pertaining to membership of, or advocacy for, a league. n. A member or supporter of a league.
Usage examples of "leaguist".
But even though they're anteing up a lot of money to Gustavus Adolphus, they're trying to hedge their bets in case he doesn't win the war—keeping a weather eye out on what the imperials and the Leaguists are doing and the possibility that this abbot could be tossed out and replaced.
Through him, of course, he can get support from Duke Maximilian of Bavaria and the Leaguists and the Imperials.