Professional sports leagues that challenged the establishment

The Negro Leagues were a series of baseball leagues that featured all African-American teams. The leagues were formed to allow black ballplayers to play professional baseball as Major League Baseball was segregated. Some of the greatest players in history (Josh Gibson, Satchel Paige , Oscar Charleston, Cool Papa Bell) spent the majority of their careers in those leagues. When baseball integrated in the late 1940s, Negro League players like Jackie Robinson, Willie Mays, Hank Aaron and Ernie Banks got to play Major League Baseball, and soon the need for Negro Leagues ended.

Popularized by the movie "A League of Their Own," the AAGPBL was established to keep baseball in the public eye and used women as many male ballplayers fought in World War II. The league was based primarily in the Midwest. Once the war ended and Major League Baseball was restored and televised, the AAGPBL dissolved in 1954.

The CBA may have been the most successful second-tier league in American history. Formed in 1946, the CBA lasted over 60 seasons and acted in the fashion that the NBA's current D-League does. While not a minor league for the NBA, the CBA was a place players could go and develop into NBA players. Coaches, like Phil Jackson, Jerry Sloan, Flip Saunders and George Karl, could gain valuable experience and net NBA head coaching jobs.

The AFL may be the most successful startup league of them all. The league was created as direct competition to the NFL by owners and markets that were turned down by the NFL. The league featured a pass-friendly philosophy that gained traction with fans and players. Quickly, the AFL and NFL got into bidding wars for talent that caused salaries to soar. The champions from both leagues then met in a championship game (the modern Super Bowl) with the NFL absorbing the entire AFL (not just a few teams) in 1970. That success is what helped the ABA and WHL form rival leagues with the intent to merge with the established league.

During the 1960s, leagues were popping up to directly challenge to stodgy, established pro leagues. The ABA was one of the more successful entities. Essentially, the ABA added flair to pro basketball with colorful uniforms, a colorful ball and colorful play. Stylish play with dunks and three-pointers caught fans' eyes. However, the league couldn't secure solid broadcast rights and looked for a merger between itself and the NBA. It happened in 1976 as the Nets, Pacers, Nuggets and Spurs (and Dr. J) joined the NBA.

Not until the MLS was created in the 1990s did soccer truly take hold in the United States. However, the NASL tried in the 1960s to make soccer huge here. It did very well in the 1970s with the league's anchor franchise, the New York Cosmos, signing the world's best player, Pele. Yet, overexpansion, rising salaries and the economy put a halt to the good times, and the league dissolved. Still, its creation eventually helped the MLS become a raging success today.

What the ABA was to the NBA, the WHA was to the NHL. The WHA did a great job servicing markets that were neglected by the NHL as well as with player contracts. Needless to say, the WHA was a thorn in the NHL's side. Like the NBA/ABA merger, the NHL absorbed four WHA teams (Edmonton Oilers, Hartford Whalers, Winnipeg Jets, Quebec Nordiques) in the merger. The Oilers brought along a young phenom named Wayne Gretzky into the NHL.

Yes, another upstart football league. The WFL filled the void left of a second-tier football league after the NFL-AFL merger. The WFL played just one-and-a-half seasons amid chaos involving money and issues with players leaving the NFL to play in the league, like pictured Hall of Famers Larry Csonka and Paul Warfield of the Miami Dolphins signing with the Toronto Northmen. The WFL was a proving ground for future NFL coaches and markets. Plus, the helmets were '70s awesome!

World Team Tennis has been around in some form since 1974. It is made up of teams with both men and women with each set played in a different format. Some of tennis's greatest players like Chris Evert, John McEnroe, Martina Navratilova, Pete Sampras, Billie Jean King, Bjorn Borg, Jimmy Conners, Andre Agassi, Evonne Goolagong, as well as Serena and Venus Williams have competed in the league. Players, as well as franchises, seem to fluctuate year to year, but the league has endured.

The MISL was a soccer league that performed in arenas. Think Arena Football League for soccer that kind of looked like hockey. When the NASL ended in 1984, the MISL was the biggest professional soccer league in the United States until the league shut down in 1992. While the league did eventually fold, indoor soccer is still played to this day and inspired indoor leagues in other sports, including the still running National Lacrosse League.

The USFL certainly tried to challenge the NFL and was doing a decent job as several high-profile players like Jim Kelly (pictured) spurned the NFL for the USFL. However, one owner wanted to change the league from a spring league to a fall one to go head-to-head with the NFL and force a merger. The owners won an anti-trust lawsuit against the NFL for just $1, and the league folded. The owner? Donald Trump.

One of the best examples of a league finding a niche by creating its own brand, the Arena Football League has thrived for 30 years by being its own thing. Taking football indoors on a field half the size with smaller rosters and two-way players, the AFL got popular enough that it even created its own developmental league. The league has had celebrity owners (L.A. Kiss, anyone?), TV deals and even a video game. Other indoor football leagues have formed to challenge it. However, hard times have hit the league of late, and only five franchises remain.

The WLAF was founded with two goals in mind: one, as a spring league to develop players and, two, as a way to introduce football into Europe. After two years with seven of 10 teams based in the U.S., the league re-established itself with all teams based in Europe. NFL Europa (it would eventually be named) did last 15 seasons and developed a few NFL players, but it was losing money and the NFL decided to fold the league in 2007.

With Wayne Gretzky traded to the Los Angeles Kings, hockey became cool in places that weren't traditional hockey markets. At that same time, rollerblading became popular. So merging the two, you got Roller Hockey International in the 1990s. The league was similar to hockey with games played on floors with players wearing inline skates and shooting a plastic puck. You could even play outdoors virtually anywhere since you didn't need an ice rink. As the inline skating fad died, so did the league.

Popularity for women's basketball was high after the 1996 Olympics in Atlanta, and two women's hoops leagues were formed: the WNBA and the ABL. The ABL was a solid league that actually had more talent but was at a disadvantage because the NBA backed the other league. The marketing might the WNBA had was difficult for the ABL to compete with, and the league filed for bankruptcy after two seasons.

The XFL was meant to challenge the NFL by putting physical play, eccentric personalities and production value, or the "fun," back in football. While interest was piqued for the opening weekend of the league, fans sharply stayed away due to poor quality of play and the feeling of disorganization. NBC pulled out of its half of the partnership with the World Wrestling Federation (now WWE), and the league folded after just one season.

Interest in women's soccer was high at the turn of the century so a professional women's soccer league was formed. Team USA stars Mia Hamm, Brandi Chastain, Michelle Akers and many more pledged their talent to the league. While a good idea with good financial backing, ratings and attendance were poor, and the league folded after just three seasons.

We've all seen acrobats, mascots and cheerleaders use a trampoline to make incredible dunks during NBA timeouts. Well, for three seasons there was a league devoted to trampoline basketball. SlamBall was televised by Spike TV and Versus during its run but didn't last long. SlamBall courts are still around all over the country but are used for birthday parties and events instead of a professional sport.

Remember the UFL? Probably not. The league played just four seasons and had no more than five teams in it at a time never really resonated with fans. I mean, can you name one team from the UFL? Trivia alert: The Las Vegas Locomotives won three of the four championships. In 2012, the UFL actually took a hiatus in the middle of the season, but the league never resumed it.

There have been several women's professional football leagues that haven't stuck, but not all leagues took the route of the Legends Football League. You may remember it best as the Lingerie Football League when it debuted in 2009. What began as a campy Super Bowl halftime event has turned into a legitimate league that has had leagues form all over the world. The uniforms may still be revealing, but the sport has been taken a bit more seriously.