Complex sentence: Royals rivalry is a Major League Baseball (MLB) interleague rivalry between the St. Louis Cardinals of the National League (NL) Central division and the Kansas City Royals of the American League (AL) Central division.
Split into simpler sentences: Royals rivalry is a Major League Baseball (MLB) interleague rivalry between the St. Louis Cardinals and the Kansas City Royals. The Cardinals are a member of the National League (NL) Central division, and the Royals are a member of the American League (AL) Central division.