Why the US Open Now Has a Heat Rule, and How It Could Change Matches

The U.S. Open officially kicked off on Sunday, bringing the world's best tennis players together for the premier sporting event at the Billie Jean King National Tennis Center in New York City. A new heat rule implemented this year will mark a significant change from years past. Read on for the details of this rule, why it was implemented, and how it may impact this year's event.

Extreme Heat Has a History of Causing Issues for Tennis Players

A recently implemented heat rule could impact the fourth tennis major of the year. The rule has been rolled out to protect players and fans from the oppressive heat that often distinguishes the end of August in New York City.

The impacts of climate change have taken their toll on the sport in recent years. For instance, tennis icon Novak Djokovic struggled so much with the heat at the Shanghai Tennis Masters tournament in 2025 that he vomited during the match. Likewise, Jannick Sinner collapsed to the ground at the same tournament after suffering from leg cramps and other severe effects due to the heat.

The Shanghai tournament saw temperatures rise to the upper 80s, equating to readings about 10 degrees over the historical average. When combined with the humidity levels hovering over 80%, the feels-like temperatures hit the triple digits. Temperatures on the tennis courts were even toastier than the heat index, creating miserable conditions for the players. Also in 2025, Arthur Rinderknech collapsed to the court due to the extreme heat, forcing him to retire from the match in Cincinnati.

The U.S. Open runs on a best three out of five set matches format. The length of the matches makes it more important to take steps to protect the competitors from the impacts of the heat. In addition to the players, the ball kids running out onto the court and the spectators also face danger when the temperature soars.

What Does the Rule Change Mean?

The Association for Tennis Professionals (ATP) is being proactive about protecting the players and fans during times of heat, implementing a new rule based on the wet bulb globe temperature. This temperature is the measurement of the heat stress in direct sunlight, going one step further than the heat index by also including cloud cover, wind speed, and sun angle. By also including the conditions on the court into the metric, organizers will get a better idea about the direct impact of the weather on the participants.

Players can take a 10-minute cooling break once the wet bulb globe temperature reaches 86.18 degrees during the first two sets of the match. The break allows players to change clothes, shower, hydrate, and receive additional coaching. Play is suspended once the wet bulb globe temperature reaches the 90-degree mark.

While the rule may inadvertently lead to momentum shifts and other changes, the ATP wants to protect the health of the players and everyone out at the facility.

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