Welcome back to the Monday Tennis Briefing, where we unpack the biggest stories from the past week on court. This week, electronic line calling stirred up controversy on clay, the Madrid Open delivered unexpected winning moments, and the wearable tech arms race took a new turn.

Electronic line calling (ELC) is now the official standard across top-tier tennis, but that didn't stop an old clay-court tradition from resurfacing at the Madrid Open: players arguing with umpires over ball marks. Alexander Zverev, Mirra Andreeva, and Elena Rybakina all called on chair umpires to check physical ball marks they believed contradicted the ELC system, which had ruled the balls in.

"This is a joke. The system is wrong. There is no such mark which is shown on the TV," Rybakina said during her second-round match against Zheng Qinwen, urging umpire Julie Kjendlie to step down from her chair. Kjendlie responded firmly: "That's what I have to go with. Now that we have live ELC, that's what we have to go with."

Since ELC was widely adopted on clay for both the ATP and WTA Tours last year, players have been educated on the deceptive nature of ball marks on the surface. The tours produced a video explaining the discrepancies between the system's readings and visible ball marks, and have reinforced this message through other channels. Clay is influenced by environmental factors and the amount of red brick dust on different parts of the court, which shifts from point to point as players slide and move. A ball that lands in can leave a mark outside the line, while a ball that lands out can create a mark that appears to catch the line.

Andreeva's disagreement offered the most insight into the player perspective. "I understand that you cannot overrule. But as players, what do we do?" she asked chair umpire Kader Nouni. The players are still learning to trust the electronic system, after being told last year that it would eliminate human error. For fans and athletes alike, the transition is a work in progress—but it's a step toward consistency, even if it sometimes feels like a step back.