not having won a championship from 1908 to 2016 (108 years) which stands as the longest championship drought in US sports history. The sport has also taken hold of fans on the West Coast, most notably the rivalry between the San Francisco Giants and The Los Angeles Dodgers. Historically, the leagues were much more competitive, and cities such as Boston, Philadelphia and St. Louis had rival teams in both leagues up until the 1950s. Notable American baseball players in history include Babe Ruth (714 career home runs), Ty Cobb (career leader in batting average and batting titles), Cy Young, Honus Wagner, Ted Williams (.344 career batting average), Lou Gehrig, Joe DiMaggio, Mickey Mantle (16-time all star), Stan Musial, Willie Mays, Yogi Berra (18-time All-Star), Hank Aaron (career home run leader from 1974 to 2007), Mike Schmidt (548 career home runs, 10 career Gold Gloves), Nolan Ryan (career strikeouts leader), Roger Clemens (7 Cy Young awards), Derek Jeter and Jackie Robinson, who was instrumental in dissolving the color line and allowing African-Americans into the major leagues. An extensive minor league baseball system covers most mid-sized cities in the United States. Minor league baseball teams are organized in a six-tier hierarchy, in which the highest teams (AAA) are in major cities that do not have a major league team but often have a major team in another sport, and each level occupies progressively smaller cities. The lowest levels of professional baseball serve primarily as development systems for the sport's most inexperienced prospects, with the absolute bottom, the rookie leagues, occupying the major league squads' spring training complexes. Some limited independent professional baseball exists, the most prominent being the Atlantic League, which occupies mostly suburban locales that are not eligible for high level minor league teams of their own because they are too close to other major or minor league teams. Outside the minor leagues are collegiate summer baseball leagues, which occupy towns even smaller than those at the lower end of minor league baseball and typically cannot support professional sports. Summer baseball is an amateur exercise and uses players that choose not to play for payment in order to remain eligible to play college baseball for their respective universities in the spring. At the absolute lowest end of the organized baseball system is senior amateur baseball (also known as Town Team Baseball), which typically plays its games only on weekends and uses