PARIS — Lorenzo Musetti was warned for unsportsmanlike conduct for kicking a tennis ball that inadvertently hit a linesperson during his French Open quarterfinal against Frances Tiafoe on Tuesday.

Unlike most top-level tennis tournaments, which rely on electronic line-calling, there are still humans on court at Roland-Garros to make rulings on whether shots land in or out.

The eighth-seeded Musetti, who won a bronze medal for Italy at the Paris Olympics and was a semifinalist at Wimbledon last year, had just dropped a game to trail Tiafoe 5-3 in the second set of their match at Court Philippe-Chatrier.

As Musetti was given balls so he could serve in the next game, he took a left-footed swipe at one and it flew into a line judge making calls behind his baseline.

The chair umpire immediately announced to the crowd that Musetti was being given a warning for a code violation. There is no penalty for an initial warning of that sort.

Soon, Tiafoe claimed that set. Musetti had taken the opener in the best-of-five-set match with a semifinal berth at stake. Neither of them has been to the final four at Roland-Garros.