Welcome back to the Monday Tennis Briefing, where The Athletic will explain the stories behind the stories from the past week on court.This week, a big change could be coming to the ATP Tour, how women’s tennis is protecting its stars, and a return to a brilliant sports city.If you’d like to follow our fantastic tennis coverage, click here.New balls for the ATP Tour, please?Throughout the past two years of top-level tennis, players on both the men’s and women’s tours have held a common enemy: The thing they have to hit over and over again, point after point, game after game, set after set and match after match.Whether too slow, too heavy, too fluffy, or in the case of the inimitable Daniil Medvedev, allegedly not round, tennis balls have come in for all kinds of criticism.Tennis' latest controversy: Are the balls round?Charlie EccleshareThe ATP Tour has responded by moving to centralize ball distribution at tournaments, bidding to have each swing — a run of tournaments in the same part of the world, on the same surface type — using the same ball by 2029. It is now trying something else: Changing one of tennis’ longest-held rules.At present, players start a match with new tennis balls. The balls are changed after seven games. From then on, they are changed every nine games. This system means players adjust their tactics (and often their string tensions on their rackets) through each stretch. Balls fly fastest and bounce highest when they are new; as they get hit repeatedly, their felt fluffs up, increasing air resistance on them and making them less lively.But at a Challenger Tour event (one rung below the main tour) next month, there will be a trial of changing balls sooner, initially after five games and then after every seven, a spokesperson for the tour confirmed.Medvedev, a former world No. 1 and the 2021 U.S. Open champion, is one of the most outspoken critics of the balls used on the ATP Tour. French Open champion Alexander Zverev and world No. 10 Taylor Fritz have also pushed for change. Players have attributed matches feeling longer and points feeling harder to end to slower and heavier balls, though tour data shows that rallies have remained stable or shortened over the past five years and whether or not a ball feels slow or not can be dependent on court conditions and a player’s game style.This trial, if implemented across the tour, would have more impact on balls that get fluffier, faster — and would also mean that tournaments would require more balls per event. But if it shrinks the ball quality spectrum that players have to account for during matches, it is likely to be well-received.How did players who have spent time in the tennis wilderness thrive in the same week?It was so nearly a perfect Greek tennis weekend. Its two stars of the sport, Stefanos Tsitsipas and Maria Sakkari, who have spent time in their own versions of the tennis wilderness in the past year or two, both reached their first finals in over a year — and one of them did it in their nation’s capital.