Sixteen-year-old American gymnast Laurie Hernandez announced just a few days ago that she would turn pro after the Rio Olympics, sacrificing a scholarship to the University of Florida. As a pro, she'll be able to take advantage of a goldmine out of reach to NCAA athletes: sponsorships.

Among the top dogs, unsurprisingly, are Nike (NKE) - Get Report and Under Armour (UA) - Get Report . Nike is taking advantage of the media frenzy: Wells Fargo (WFC) - Get Report analyst Tom Nikic wrote in a note that the company intends to use the Olympics as a "launching pad for innovation."

"While we believe the Games are a negative near-term catalyst, the success of the company's new innovations later this year would play a key role in the company's ability to grow the top line and fight off intense competitive pressure [from rapidly growing peers such as Adidas and Under Armour]," Nikic concluded.

Nike makes the uniforms that the U.S. athletes will wear on the awards platform, while upstart rival Under Armour nabbed star Olympians like Michael Phelps, possibly the most dedicated Olympian ever, as well as longtime reps like tennis' Andy Murray.

Olympic sponsor Visa (V) - Get Report is the "exclusive payment card and the official payment system for the Olympic Games," the only payment method besides cash that works at the Games. The credit card company sponsors about 50 athletes from all over the world, including American swimmer Missy Franklin and beach volleyball player Kerri Walsh Jennings, as well as the Olympics' first-ever team of refugee athletes.

Franklin, Walsh Jennings and others appear in Visa's Olympics TV spot, "The Carpool to Rio."

Besides the usual suspects, Deloitte's sponsored athletes include swimmer Cullen Jones and the para-equestrian dressage team. Privately held yogurt company Chobani sponsors several high-profile athletes, including track and field's Allyson Felix and soccer's Morgan Brian and Alex Morgan.

It's easy to wear your Nike-sponsored sneakers, but the athletes frequently use social media to plug their less-visible sponsors. Gymnast Gabby Douglas, sponsored by Procter & Gamble's (PG) - Get Report Gillette razors, tweeted a photo of her Rio luggage with a prominently placed Gillette razor. Alex Morgan, who has appeared in Chobani commercials, tweeted that she's "proud to partner with a brand that's truly part of my training."

Visa, Wells Fargo and Procter & Gamble are holdings in Jim Cramer's ActionAlertsPLUS Charitable Trust Portfolio. Want to be alerted before Cramer buys or sells V, WFC or PG? Learn more now.

The International Olympic Committee has made sponsorships a bit easier through changes to its Rule 40. Rule 40 favors the big official Olympic sponsors, like Visa, McDonald's (MCD) - Get Report , and Coca-Cola (KO) - Get Report , over companies like Chobani, which sponsor individual athletes rather than the games as a whole.

For the first time this year, those sponsors can run ads during the so-called blackout period (running July 27 to August 24) using their athletes, as long as they don't specifically mention the Olympics. Previously, only the official sponsors could run ads at all during the Olympics, and the athletes couldn't mention their individual sponsors.

Rule 40 is why Michael Phelps' Under Armour TV spot shows him training in and out of the pool but never mentions the Olympics or Rio. It's also why a Virgin Media ad for Jamaica's Usain Bolt, the world's fastest man, highlighted his world-record 100-meter sprint time at the Berlin running world championships in 2009.

American runner Emma Coburn thanked her sponsor on the last day before the blackout period. "#Rule40 starts tomorrow so I won't be able to say Thank You to my sponsor. THANK YOU FOR EVERYTHING @newbalance," she wrote to privately held sneaker manufacturer New Balance on July 26.

Sally Bergesen, the CEO of running apparel company Oiselle, wrote in a blog post that her company decided not to run Olympic ads because the United States Olympic Committee demanded too many changes.

"Despite the loss of focus, relevance and respect, we decided to create and submit a campaign anyway," she wrote on July 21. "After some back and forth ('please dilute further,' and 'do not use Team USA' for an athlete who had been on Team USA), the below campaign was approved. Come March 2016, we decided to not start running the campaign. Because it is generic and non-relevant, it is not effective enough to justify the cost."

Of course, plenty of athletes don't turn pro. American swimmer Katie Ledecky, considered one of the best athletes in the world, still plans to swim for Stanford starting this fall. A sports industry analyst told the New York Times Magazine that Ledecky would have earned big money as a sponsor.

"She has a terrific personality -- great kid, great smile, she's excelling at a really high level," Matt Powell of NPD Group told the Times Magazine. "The endorsement side could be worth millions to her, as much as $10 to $15 million per year."

Hernandez's teammate on the gymnastics team, 19-year-old Madison Kocian, is also eschewing lucrative sponsorships to maintain her NCAA eligibility and compete for UCLA in the fall. Kocian is the only one of her teammates not to go pro. Possibly not coincidentally, she's an uneven bars expert who competes in fewer events than her teammates and is likely to take home fewer medals.