Prediction markets like Kalshi and Polymarket allow traders to buy and sell "event contracts" on the future of nearly anything. The rapid growth of these markets–regulated by the Commodity Futures Trading Commission–has ignited a fierce legal battle with state attorneys general and gambling regulators over whether sports betting contracts should be allowed. WSJ explains how prediction markets work and what is at stake in the legal battle that threatens the future of the industry. Chapters: 0:00