the tennis world awoke to a surprise on Monday, with Aryna Sabalenka replacing Iga Swiatek as No. 1 in the WTA rankings.

Sabalenka, who has won two Grand Slam titles in a sterling season, has been engaged in a battle for supremacy with Swiatek — who has a Grand Slam title of her own, and five titles in 2024 to Sabalenka’s four — all year. It was expected to run until the season-ending WTA Tour Finals in Riyadh, Saudi Arabia, next month, where Swiatek is defending champion.

Instead, Swiatek lost 120 ranking points in the latest update, and Sabalenka lost 10, leading to her leapfrogging her rival to start her ninth career week as the top-ranked women’s tennis player in the world.

But neither player took part in a tournament last week, so what happened?

Why did Swiatek and Sabalenka lose their ranking points?

Under WTA rules, players must enter and play six WTA 500-level tournaments per season. If a player is involved in fewer than that, they lose the ranking points they earned from their worst results of the season across all tournament categories as punishment — not just from the 500-level events they did play in.

The Pan Pacific Open in Tokyo is the only WTA 500 event left this season and that starts today (Monday, October 21), with Swiatek having played two 500-level events and Sabalenka four: