Maria Sharapova. Image via Tim Wang, Flickr.

Forbes released its annual list of the world's highest-paid athletes last week, and just three women made the top 100. That's the same number as 2013, and an increase from 2012, when only two made the list. The Women's Sports Foundation reveals women in professional basketball, soccer, and golf typically make between 60% and 95% less than their male counterparts, and aside from its Grand Slam tournaments, tennis fosters a similar disadvantage.

The evidence is clear: The gender pay gap exists in sports, too. And it's an issue that's as complex as it is troubling.

Popularity may play the biggest role
According to a Harris Poll, none of the 15 most popular sports in the U.S. are exclusive to women. Approximately 35% of Americans say the NFL is their favorite sport to watch, followed by the MLB at 14%, and college football at 11%. Tennis, the country's favorite women's sport, is behind swimming, and, yes, the Professional Bowlers Association. Altogether, less than 3% of the U.S. calls any of the five major women's sports -- tennis, college basketball, pro basketball, soccer, and golf -- its favorite.

So what about the money? Naturally, fewer fans translate into less revenue. The LPGA Tour, for example, makes around $60 million a year while The PGA Tour takes in close to $1 billion. The NBA's financial footprint, meanwhile, is nearly 50 times larger than the WNBA's. And in tennis, the men's ATP World Tour almost always takes in more annual revenue than the women's WTA Tour.

A lack of financial success in comparison to men's leagues is the most sensical explanation of why the pay gap exists in sports. However, the reason why we, as a culture, ignore female-dominated athletics is a philosophical debate with a range of theories. Perhaps it exists because of a lack of media coverage, or it's possible gender stereotypes are to blame. 

Digging deeper
On Forbes' latest rankings, the three women who made the cut did so almost entirely because of their sponsorships. Maria Sharapova, Li Na, and Serena Williams all made at least $11 million from sponsors last year. Sharapova and Li took in close to $20 million. That about rivals what Cristiano Ronaldo ($28 million) and Lionel Messi ($23 million) made from sponsors, and both footballers finished in Forbes' top 10.

It's tough to predict when, or if, a day will come when female athletes are given contracts that rival the salaries of LeBron James or Peyton Manning. But endorsements might be another way the pay gap can begin to be corrected. The issue is that to this point, women have been severely under-marketed in this arena.

Mary Lou Retton, a former U.S. Olympic gymnast, shared her thoughts in ESPN's "Branded" last year: "There are two categories [of female athletes]... Wholesome, all-American, squeaky-clean, or sexy vixen. Why is our society today like that? Why do women have to be like that and the men don't?"

Ultimately, this dichotomous view limits the number of sponsorship opportunities available. Stacy Lewis, the world's top ranked women's golfer, and the WNBA's Diana Taurasi are just a couple examples of dominant female athletes who don't fall squarely into either category -- and neither have endorsement deals that come close to Sharapova's.

The big question
So, will marketers ever open their eyes? Given that between 30% and 35% of most sports' fan bases are women, according to Nielsen, the raw numbers reveal they should. Kevin Adler, a sponsorship expert and founder of Engage Marketing, explained in Women's Wear Daily how companies could incorporate female athletes:

Quite frankly, there are a lot of brands that have overlooked the marketability of female athletes....The combination of strength and beauty is a very aspirational message that brands can use, especially those targeting young female consumers.

Opendorse, an athlete endorsement marketplace with clients ranging from Adidas to Best Buy, shares a similar sentiment. In its latest Endorsement Marketing Trend report, it predicts that "as more women increase their influence and marketability through social media outlets, more [will sign] endorsement deals."

The bottom line
"The days of solely relying on male athletes to endorse products are extinct," Opendorse adds. And with Sharapova, Li, and Williams, in addition to rising stars like Lewis, this proclamation isn't outlandish.

It's tough to forecast if one day, a league like the WNBA or LPGA will be as popular as their male counterparts. But speaking from personal experience, women's sports are just as exciting, entertaining, and athletically impressive to watch. Here's hoping more fans -- and sponsors -- will recognize that.

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