Tennis has always treated the weather as background noise. Until that noise took over the centre of the court. Shanghai, October 2025: a string of retirements, cramps, nausea, players emptied out by the air more than by the opponent. It was not an isolated episode. It was a public reminder that, in certain weeks, “extreme conditions” are not an accident. They are the setting.
From 2026, the ATP changes its language: not “it’s hot” but “it’s measured”. A Heat Policy comes into force based on WBGT (Wet Bulb Globe Temperature), with numerical thresholds, procedures and responsibilities written down. The ATP sells it as standardisation but the side effect is more interesting: it turns heat into regulation, then into governance, then into conflict.
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WBGT, or the end of “32 degrees, full stop”
WBGT is not a decorative acronym. It is a heat stress index designed to estimate how hard the body is working to shed heat in full sun, combining temperature, humidity, wind and radiant heat. It is exactly the kind of metric that makes thermometer simplifications instantly useless.
In plain terms: two days at “30 degrees” can be two different sports. One is brutal. The other is dangerous. In 2026, the ATP at least stops pretending that counting degrees is enough.
Two thresholds that change the match
The 2026 Rulebook defines four operational bands but the only numbers that really matter are two:
WBGT ≥ 30.1°C: Extreme Heat Level 1
WBGT ≥ 32.2°C: Extreme Heat Level 2
For completeness, the scale also includes Normal (WBGT < 29.0°C) and Heat Advisory (29.0–30.0°C), even if the match-changing thresholds are the two extreme tiers.
It looks like a medical protocol. In reality, it is also a new match grammar.
Level 1: the break exists, but it does not trigger on its own
If WBGT is at least 30.1°C before the third set (best-of-three singles), “either player may request a Cooling Break”. One player can ask for it and it automatically applies to both. It lasts 10 minutes, measured from the end of the second set to the start of the third. In those ten minutes, what matters is getting a body back online: shower, change of clothes, hydration, cooling measures, coaching under ATP rules and medical supervision.
The detail that deserves a headline, though, is another one: the break is a player choice.
This is where tennis complicates its own life. Because “you may request” in already extreme conditions means this: protection becomes a tactical decision. If you are in front and rolling, stopping the match can be a gift. If you are behind and falling apart, the break is a crutch. The rule does not impose a medical intervention. It offers a piece of match management.
The ATP has created a point where health and competitive advantage sit on the same menu. No moralising needed. Just look at the structure: the rule says “you can” while the match asks “should you?”.
There is a second, sharper irony: the break is “system-approved” but enforced with a whip. If a player returns late, Time Violations stack up, then a point penalty follows for subsequent offences. It is an exceptional concession run with ordinary discipline.
It is worth noting what the rule does not do: doubles gets no formal Cooling Break, only a possible 90-second hydration extension at set breaks once WBGT reaches 31.0°C.
Level 2: automatic stoppage, but with a stopwatch
When WBGT reaches 32.2°C and stays there for 15 consecutive minutes, the Supervisor must suspend play on all outdoor courts. Not “may”. Not “will consider”. Not “will consult”. The current game or tiebreak is completed first.
Again, the key detail is the mechanism: a spike is not enough. It needs continuity. The restart is stricter still: play only resumes when WBGT stays below 30.5°C for 20 consecutive minutes, with a formal restart notice to stakeholders.
On paper, this is the easy part: stop, then go. In practice, it can cripple a tournament because it drags in scheduling, broadcast commitments, ticketing and the compression of recovery windows. If the stoppage lasts for hours, the protocol is no longer managing a difficult moment. It is managing an entire day of the event.
The roof: technology as hierarchy
Then there is the chapter that looks neutral but is pure politics: retractable roofs.
The Rulebook says the roof must be closed if WBGT is at least 32.0°C or if the court surface temperature is at least 45°C. The closure happens at a change of ends or at the end of a set, it is treated as a suspension of play and once closed, it stays closed until the end of the match.
Interesting geometry: roof at 32.0, general stoppage at 32.2. The most effective protection kicks in earlier, but only where the infrastructure exists. That is unavoidable. The outcome, though, is a tournament split into two ecosystems: those playing “inside” and those waiting “outside”. Same event, non-comparable conditions.
And when there are one or two roofs, the question is obvious: who gets it? The answer is just as obvious: the televised match. Everyone else sits in the queue, with a rule designed to protect but unable to guarantee structural fairness.
The real problem: when “extreme” is normal
The Heat Policy is credible when it handles a rough couple of hours. It becomes fragile when parts of the calendar start to look like a scheduled interruption.
If WBGT repeatedly crosses the thresholds for half a day, every option is bad:
Split the day into two windows: early morning and evening, with a huge dead zone in the middle. Logical on paper, brutal for logistics and recovery.
Build a stop-start backlog: suspend and restart, suspend and restart. The fastest way to make preparation unmanageable.
Treat the roof as a privilege: move what you can, which is not much, then decide who “deserves” better conditions.
Rewrite the calendar: the only serious solution and the one nobody wants to touch.
If a policy triggers every day, it is no longer an exception. It is a permanent plaster. At that point the question becomes unavoidable: why keep playing there, at that time of year, as if it were a minor inconvenience?
Transparency: if a number decides, that number must be visible
In the Rulebook, WBGT is “taken or confirmed on-court” by the ATP medical team together with the tournament doctor.
Fine. Now the point is this: the value must be public. On the scoreboard, on the broadcast, in official updates, with timestamps. Not for entertainment, but to remove ambiguity. In tennis, every unexplained decision turns into suspicion within minutes: “why here but not on the court next door?”, “why now?”, “why exactly when someone was building a comeback?”.
If the Heat Policy is meant to reduce controversy, it cannot create a decisive metric then treat it as an internal reading.
Heat as a system test
The ATP has done something it should have done years ago: it has stopped leaving everything to moment-by-moment discretion and has put thresholds and procedures on paper.
But the story is not “a new rule arrives”. The story is what the rule exposes.
Level 1 dumps an impossible choice on players: protection versus momentum. Level 2 can paralyse a tournament if the weather offers no workable windows. The roof introduces an inevitable but visible inequality. Above all, the core issue remains, the one no protocol can hide for long: there are weeks where tennis is scheduled against physiology.
Heat is no longer just weather. It is regulation. Once it becomes regulation, you can no longer sell it as an unforeseen disruption. A policy that stops play every day is not protection. It is an admission of bad scheduling.
BOX SLAMS
The ATP is standardising WBGT across its own tour events from 2026. The Slams remain a patchwork. Melbourne runs the AO Heat Stress Scale. Wimbledon uses a WBGT-based heat rule (10-minute break at WBGT ≥ 30.1°C). The US Open operates its own Extreme Heat Policy. In Paris 2024, the ITF used a WBGT trigger for a 10-minute break on the Roland-Garros courts, but governance is not unified across the calendar.
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