Two matches in the 2026 World Cup's opening round were played in heat conditions that the global players' union Fifpro previously said should trigger delays or postponements. Saudi Arabia's match against Uruguay in Miami had the most severe heat conditions of the opening 24 matches, while Sweden's game against Tunisia in Monterrey was the second-most severe among stadiums without air conditioning.
Both matches reached wet-bulb temperatures of 28°C (82°F) or above despite evening kick-off times. Wet-bulb temperature combines air temperature, humidity, and cloud cover to measure the body's capacity to cool through sweating. Beyond this threshold, sweat cannot evaporate properly, resulting in rapid overheating that may cause illness or death.
Fifpro has previously stated that matches played at 28°C or above should be delayed or postponed. Four additional games were played in cities exceeding this threshold, though air conditioning in their stadiums mitigated conditions inside. The 2026 tournament is forecast as the hottest World Cup since the competition began in 1930.
Extreme heat accelerates player fatigue and increases injury risk, potentially affecting markets that price match outcomes based on squad depth and physical conditioning. Teams with stronger benches may gain tactical advantages in such conditions.