"This is such a disappointing decision, US OPEN" — that was tennis analyst Jon Wertheim's verdict on the US Open's exclusive agreement with the prediction platform Kalshi. The deal shuts rivals out of the tournament's broadcasts and its arenas altogether, Polymarket among them. It is a strange paradox. At the very moment the International Tennis Integrity Agency is handing player Mila Masic a four-year, 10-month ban for fixing her own matches, the tournament is taking sponsorship money from a platform that trades on insider information. Kalshi does offer strict security guarantees, yet the conflict of interest remains plain to see. Prediction markets are becoming an inseparable part of modern sport. In this new era, striking a sensible balance between financial innovation and the integrity of the court is emerging as the most important challenge of all.