Remove domes and evening kickoffs from the group-stage heat table and most teams drop to zero. France is the only favourite with all three games in open-air afternoon sun. Brazil, Argentina, Spain, Portugal and the Netherlands carry no open-air afternoon heat load at all.

WBGT — wet-bulb globe temperature — is a single number that combines air temperature, humidity, wind and radiant heat from the sun. It is the standard heat-stress index used by FIFA and sports-medicine bodies to decide when conditions are dangerous for players. Above roughly 28°C WBGT, cooling breaks become mandatory; above 32°C, postponement is on the table.

France-Senegal had 20°C drizzle at MetLife; England had 35°C clear sky at roofed Dallas. Same raw heat tier, different football exposure.

Before the tournament, a pre-committed WBGT grid for all 104 kickoffs put France on 76, Uruguay on 74 and Brazil on 69 — close enough to hide three different football exposures. ¹

Strip out closed domes and evening starts and the table changes. France stays at 76. Uruguay drops to zero because all three group games are evening games. Brazil drops to zero. Argentina, Spain, Portugal and the Netherlands land on zero open-air afternoon load.

The group stage is testing the split

France’s schedule puts all three matches in the open-air afternoon window: Senegal at MetLife on June 16th at 3 p.m. ET, Iraq at Philadelphia on June 22nd at 5 p.m. ET, and Norway at Boston on June 26th at 3 p.m. ET. ²

The opener landed mild. MetLife on June 16th recorded 20°C with light drizzle — well below the WBGT stress threshold. France pressed hard, ran 120.2 km as a team, recorded 533 sprints and 9.8 km of sprint distance, and completed 88.4 percent of their passes in a 3-1 win. That is baseline data — high-intensity numbers from an afternoon match without heat stress.

Philadelphia on June 22nd and Boston on June 26th are the test. Both are named in peer-reviewed venue modelling as sites that exceeded 28°C WBGT in the 2003 to 2022 record, with the highest uncompensable-stress risks coming in the afternoon. ^{4 5}

If France’s sprint count, sprint distance or high-intensity running drops at Philadelphia or Boston while pass completion holds or rises, the heat split is showing up in the football.

Why roof and kickoff matter more than raw totals

FIFA allocated venues and kickoff times with player welfare, average temperatures, cooling infrastructure and venue technical analysis as stated factors. England v Croatia went to Dallas and Curaçao v Germany to Houston — roofed or climate-controlled conditions for early local kickoffs. ³

England’s Dallas match recorded 35°C outside with clear sky, but the team played under a roof. A roofed Dallas afternoon and an open Philadelphia afternoon can produce similar raw tournament totals, but only one of them is real heat exposure.

Squad-to-squad comparisons need roof and cooling decisions in the team heat table. Without the split, England and France look like they carry similar group-stage heat loads. After the roof and cooling split, France’s load is real while England’s Dallas number comes from outside conditions, not the playing environment.

What heat does to the football

High environmental stress changed how teams ran and passed. At the 2014 World Cup, 16 of 64 matches were played under high environmental stress. Sprint count was 10 percent lower than in low or moderate stress, high-intensity distance fell, and pass success rose from 73.6 percent to 76.8 percent. ⁷

In controlled trials at 43°C versus 21°C, total distance fell 7 percent, high-intensity running fell 26 percent, pass success rose 8 percent, cross success rose 9 percent, and possession time rose from 21.2 minutes to 26.5 minutes. The hot game also had fewer ball gains, fewer ball losses and fewer duels. ⁸

Heat reduced sprinting and shifted teams toward longer possessions, safer passing and fewer transition contests. A pressing team that relies on sprint volume and forced turnovers loses more from heat than a possession team that circulates at walking pace. ⁹

The hydration-break segments

Every 2026 match gets a three-minute hydration break 22 minutes into each half, regardless of weather. ⁶ Those stoppages mark four fixed periods to compare — kickoff to the first break, first break to half-time, restart to the second break, and second break to full time.

A break inside a controlled stadium and a break at 3 p.m. in Philadelphia carry the same timestamp and different thermal evidence. Sprint counts, high-intensity distance, ball gains, losses and duels split by segment will show whether a team fades after the second break or manages intensity evenly across all four.

France’s MetLife data is the baseline. Compare each segment’s sprint count and pass completion against the same segments at Philadelphia and Boston. If the post-break segments show steeper drop-offs in the hotter venues, the heat is changing the football in the second half of each period.

Acclimatization and the knockout draw

Heat readiness depends on recent training exposure, not birthplace. Senegal had 23 of 26 players coming from European club seasons, with only Mané and Mendy arriving from a hot Saudi league. ¹

A 14-day heat-acclimatization camp drops resting core temperature by about 0.47°C, trends plasma volume up 7.4 percent, and improves heart-rate recovery in small-sided games. ¹⁰ The optimal window is 10 to 15 consecutive days of exercise-based heat exposure. ⁹ France trained in Nantes before flying to Boston with about five days before the opener and no reported warm-weather camp. ¹

The knockout draw will assign new venues to teams that survived the group. A team that played three evening games and advanced with zero open-air afternoon load could draw a 3 p.m. kickoff at an open stadium for the round of 16. Their raw group WBGT would not have predicted that exposure, but the dome-and-evening split would have flagged them as untested.

The split method stays the same as the tournament moves forward. Strip domes and evenings, compare what remains, and check the sprint and possession data by hydration-break segment. The group stage is producing the baselines. The knockouts will test them.