The four major professional leagues were perfectly content to maintain their monopolies until guys like Dennis Murphy showed up and turned sports upside down -- and as a kid, I loved it.
The Continential League never played a game, but forced the AL and NL to expand into places like Minneapolis, Houston and Atlanta, then eventually to Denver and Toronto. The Mets were offered to the CL ownership led by Joan Payson after the Dodgers and Giants left town.
The ABA and WHA struggled from the start, mainly because of the economic downturn that plagued the entire decade of the 1970s, but were way more fun to watch than the established leagues. I remember seeing Rick Barry with the Anaheim Amigos, and the Howe family with the Houston Aeros. Basketball doesn't get to Indianapolis, San Antonio and Denver -- and the NBA doesn't expand as rapidly -- without Murphy. Same with the NHL, which resisted expanding past the Original Six for way too long.
Plus, Doctor J and Wayne Gretzky revolutionized their respective games while playing in the upstart leagues.
In addition, you had the American Soccer League and NASL starting up. Just an explosion of new teams and leagues right when I was getting interested in different sports.
World Team Tennis was a pretty radical idea for its day, and rode the coattails of the tennis boom surrounding Evert, Connors, King, et al. Plus you can't really underestimate the significance of the Riggs-King match, which happened to be played on my birthday.
RIP to a visionary.