Serena Williams' ex-coach Rennae Stubbs gives her verdict on Alexander Zverev’s Madrid Open line-call controversy

Serena Williams' former coach, Rennae Stubbs, expressed her views on Alexander Zverev's bout with the electronic line judge employed at the 2025 Madrid Open. While the Aussie agreed with the German on the line-calling system being susceptible to mistakes, she conceded in the same breath that his opponents in Madrid could've also suffered the same fate.

Zverev expressed his displeasure with the electronic line-calling system in back-to-back matches at this year's Madrid Open. The first incident where the World No. 2 was not in favor of the technology happened in the second set of his third-round victory against Alejandro Davidovich Fokina when the Spaniard hit a backhand slice approach seemingly wide, but the electronic line judge called it in.

Alexander Zverev was admittedly frustrated at the above call as he implored the chair umpire to take a look at the ball mark. The top seed expressed disagreement with the electronic line-calling system once again during his fourth-round match at Caja Magica on Tuesday (April 29) when it called his opponent Francisco Cerundolo's first serve in. Since the 28-year-old believed the ball to be out, he complained to the umpire before eventually losing the match in straight sets.

On the latest episode of her podcast, Rennae Stubbs Tennis Podcast, Rennae Stubbs agreed with the German when it came to the first ball mark having been well outside the singles court. That said, the 54-year-old also offered some fresh perspective on the line-calling controversy.

"This ball was out, clearly out. Ball mark showed out, there's no other ball mark around... this was an absolute pure mistake by the machine that, guess what? Happens all the time in the human world. That same mistake or that same call might happen to your opponent the next game, right?

"So, you know, in a lot of ways that electronic line call is going to f*** it up maybe the same way the next time around. So it's even-stevens, whereas a human might interpret it one way or the other."

During the podcast, Stubbs also related with Alexander Zverev's reaction to the electronic line-calling system compromising his prospects of winning matches. However, she reiterated her above stance on the topic while talking about the "human error" aspect of it.

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Serena Williams' ex-coach Rennae Stubbs: "Would I have lost my mind as of Alexander Zverev? Abso-f***ing-lutely"

Alexander Zverev looks on at Madrid Open 2025 | Image Source: Getty

Rennae Stubbs pointed out that machines were just as capable of making calibration errors as umpires were of having a lapse in their judgment. The former player-turned-coach also asserted that the electronic line-calling system wasn't targeting Zverev in particular.

"Would I have lost my mind like Alexander Zverev? Abso-f***ing-lutely. But the difference is that it's not a human error, it's a calibrations issue," she added. "Probably with the machine, that they can fix and it's going to happen to your opponent more than likely in the same match. So I'm a little bit less pissed off at the electronic line calling, in general, because I just feel like it's there's no human error on that."

Alexander Zverev, meanwhile, will now be looking to get some rest before his Italian Open title defense next week.