The US Open, the fourth tennis major of the year, could see impacts both positive and negative from a new heat rule implemented in 2026.

This rule was established to protect the players, ballkids and fans from oppressive heat during tennis matches.

Why the change?

It became obvious that men's tennis players were suffering in extreme heat in certain tennis tournaments. The Shanghai Tennis Masters tournament in 2025, which took place in late September and early October, was brutal in terms of heat. Novak Djokovic, seen above, struggled with the heat and even vomited before eventually winning his match.

Weather in your inbox

Forecast Location

Sign Up

By signing up you agree to the Terms & Privacy Policy. Unsubscribe at any time.

Jannick Sinner also struggled with the heat this tournament, suffering from leg cramps and heat-related illness.

In fact, there were numerous players who retired from their matches due to heat, including Casper Ruud, Tomas Machac, David Goffin, Terrence Atmane, Hamad Medjedovic and Wu Yibing. The temperatures were often in the mid to upper 80s that week, which was about 10 degrees above average. Factor in humidity above 80%, and the feels-like temperature peaked around triple digits.

And the temperatures on the tennis court are often even hotter than the heat index, due to the fact that tennis courts absorb heat as well.

Get More of Our News on Google

Set The Weather Company as a 'Preferred Source' to get quicker access to the news you value.

But it wasn't just this tournament. At Cincinnati in 2025, which took place in mid-August, Arthur Rinderknech collapsed on the court in the extreme heat and was forced to retire from his match.

These tournaments are just best two out three set matches, and the four majors of the year, including the US Open, are best three out of five set matches. These rules are even more important to add for the majors.

And it is more than just the players. Ballkids are also running on the court and are not trained, professional athletes. These children also can experience heat-related illness due to the extreme temperatures on the court. Also, for fans, some of the courts don't have roofs. Those who are watching matches on the uncovered courts are experiencing the same brutal heat as the players.

What is the change?

The Association for Tennis Professionals is now implementing a rule based on the wet bulb globe temperature. This measures the heat stress in direct sunlight.

It basically goes a little further beyond just the regular heat index, which is the temperature it feels like when humidity is factored in.

The wet bulb globe temperature does include temperature and humidity, but also includes conditions on court that will directly impact the players. These include sun angle, cloud cover and wind speed.

What are the levels, and how will this change the sport?

When the wet bulb globe temperature hits 86.18 degrees during the first two sets of a best-of-five match, a 10-minute cooling break is allowed. This means that players can cool off in ways like hydrating, changing clothing, showering and receiving coaching.

If the wet bulb globe temperature hits 90 degrees, then play is suspended.

This change has the potential to change the sport pretty drastically, especially for the four majors each year. Men's tennis plays first to win three sets out of five, so these cooling breaks and suspension of play can lead to major momentum swings.

The players will have another mental hurdle to overcome, but it is for the sake of physical health that these rules are implemented.