Sports are a big part of prediction markets. So big that even sportsbooks have moved into the business. While some leagues are cashing in, others are taking a more cautious approach. The rapid growth of sports offerings on prediction markets — called event contracts — has captured the attention of the four major North American sports, along with the NCAA and other organizations. Kalshi and Polymarket are the two biggest platforms, but they have plenty of company. More are on the way, too. Almost eight years after a Supreme Court ruling cleared the way for legalized sports gambling across the country, the increased presence of prediction markets has received a mixed response in sports.