2021 WTA Finals in Guadalajara will be using pressureless balls. The reason for using pressureless balls is that Guadalajara, Mexico is about 5100 feet above mean sea level. At such a high altitude, air pressure is lower, and regular tennis balls can be difficult to control.

World number 1 Ashleigh Barty pulled out of the WTA finals for many reasons. One reason cited by her coach Craig Tyzzer was the ball to be used at the tournament.

Pressureless balls fly. If you use such a ball under normal conditions, it will not bounce. I don’t think it’s the best publicity for the best women in the world to play with something that they have never tried before. Under conditions that they do not know, in a country where they have not yet played and at this altitude. That just feels ridiculous.

– Craig Tyzzer

When asked about playing with pressureless balls, Iga Swiatek said:

I have no idea. I have to try this. I played in Madrid for the first time this year, and my shots were flying like crazy. So we made some adjustments, and by the end, I played really solid tennis. Guadalajara is going to be even worse, so I really need to get used to the conditions.

But Guadalajara was the only option available to the WTA for hosting the year-end finals after Shenzhen refused to host the event due to COVID-19 rules. But playing such a prestigious tournament using pressureless balls can make watching tennis unattractive for fans due to the high number of errors players are likely to make playing with pressureless balls.