Sydney Sweeney to LeBron: Prediction Markets Bet on Star Power

Sydney Sweeney has a new job title. On September 9, sports prediction platform Novig unveiled its first national campaign built around her, a "Just Sports" push meant to draw a hard line between Novig's sports-only trading and the everything-under-the-sun approach of rival prediction markets Kalshi or Polymarket that dabble in politics and pop culture. Novig didn't just hire Sweeney. It made her a strategic partner and equity holder, which turns a celebrity spot into something closer to a co-founder credit.

Sweeney is a headline, but she isn’t an outlier. Prediction markets have spent the past year building out a celebrity roster that would make a Super Bowl ad buyer blush, and the money behind it explains why.

Why Are Prediction Markets Spending So Much?

Kalshi and Polymarket, the two biggest names in the category, are each valued at roughly $20 billion. Polymarket has now reportedly completed a $1 billion round at a $21 billion valuation while Kalshi closed a $1 billion raise in May at a $22 billion valuation. Kalshi is reportedly shopping a new round at an even more staggering $40 billion valuation.

Both platforms are also stacking league partnerships that come with built-in audiences: the NHL signed multiyear deals with both, MLB named Polymarket its exclusive prediction market exchange and paired it with a CFTC integrity agreement, and Kalshi struck a data partnership with CNN.

Sports contracts drive a huge share of trading volume on both platforms, so the marketing budgets follow the sports calendar. Celebrity ad blitzes now land right before football season and the World Cup, and it sure as hell isn’t an accident.

Who's Promoting Prediction Markets?

Novig's roster starts and mostly ends with Sweeney, since the platform only launched nationwide last month. Kalshi and Polymarket have been building for longer, and the list is long enough that it's easier to track by platform than by trying to rank five names.

Kalshi has leaned on sports royalty and star power across generations: tennis great Pete Sampras and Marshawn Lynch fronted new ads timed to the U.S. Open, Giannis Antetokounmpo joined as a shareholder and became the first basketball star to do so, and Bryson DeChambeau became the first athlete of any kind to sign with the company, a deal only possible because he plays on LIV Golf rather than the PGA Tour. Kalshi also tapped Timothée Chalamet for a run of offbeat shorts set in places like a dentist's office, and brought in reggaeton star J Balvin for a World Cup-timed spot. Its international soccer push went even further: Lionel Messi appeared in a partnership with Argentina's federation alongside teammates Rodrigo De Paul and Nicolás Otamendi, while Luka Modrić became a face of Kalshi's tie-up with Croatia's federation.

Polymarket answered with sheer volume. Its LeBron James-fronted commercial, directed by Peter Berg, imagines Polymarket's headquarters as a skyscraper where every floor represents a different market, and James's tour of the "sports floor" turns into a parade of cameos: Derek Jeter, Eli Manning, Sue Bird, Richard Sherman, Rajon Rondo, Reggie Bush, Bob Stoops, Spike Lee, Emily Ratajkowski, Alexandra Daddario and John Leguizamo all show up. Eagles running back Saquon Barkley has invested in Polymarket but hasn't appeared as an endorser, a distinction that matters given how the NFL treats the category.

Between the two, that's dozens of names spanning basketball, football, tennis, golf, soccer, music and film. A category that marketed itself two years ago as a tool for forecasting elections is now running the exact playbook sportsbooks perfected a decade ago.

How Much Are These Deals Worth?

Most of these arrangements are undisclosed, and it's worth resisting the urge to guess. Sweeney holds equity in Novig, and Antetokounmpo is a Kalshi shareholder, meaning both have upside tied to company performance rather than a flat appearance fee. Chalamet's deal has been reported by entertainment outlets at around $1 million, though that figure remains unconfirmed by Kalshi. Beyond those, contract length, campaign spend and individual payouts remain private on both sides.

Who Won't Promote Prediction Markets?

Not every league is on board with the prediction market boom. The NFL Players Association has told reporters directly that its gambling policy bars players from endorsing or acting as a brand ambassador for a company like Kalshi or Polymarket, full stop. The PGA Tour hasn't approved prediction markets as a sponsorship category at all, which is precisely why DeChambeau's deal only works while he stays on LIV Golf. MLB sent players a memo this year warning that trading on baseball-related contracts violates its existing sports betting policy, though the league hasn't said whether endorsement deals are separately restricted. The NBA sits in the middle. It has no blanket ban on players partnering with prediction markets, but no promoting NBA-specific contracts, the same line it draws with traditional sportsbook deals.

Documented public refusals from individual celebrities are hard to find. The pushback so far has come after the fact. Both the Sweeney and James campaigns drew immediate backlash on social media over "selling gambling" through star power, and the industry's murky legal status isn't helping: a Ninth Circuit ruling in August said Nevada could enforce its gambling laws against Kalshi's sports contracts, and the broader fight over who regulates prediction markets could reach the Supreme Court as soon as next year.

Prediction markets used to sell themselves on politics, forecasting, and the thrill of being right before anyone else. That pitch still exists, but it's been buried under the same star-studded playbook online casinos and sportsbooks have used for years: famous faces, big budgets and campaigns timed to whatever season is about to kick off. Sweeney may be the newest name attached to it, but she's already got plenty of company.