Tennis Has a Rule for When the Net Gets in the Way

At the 2016 US Open, an umpire called a let on a Jerzy Janowicz serve against Novak Djokovic. Replays showed the ball had cleared the net cord by several inches. The electronic sensor system disagreed, and under the rules, the sensor's call stood. The point was replayed anyway.

That's the let rule in miniature: a piece of tennis law old enough to predate electronic officiating entirely, still capable of overruling what everyone in the stadium just watched with their own eyes.

What is a let in tennis?

A let is any instance where a point gets replayed rather than counted as won, lost or faulted. The most common version is the service let: the ball clips the net cord on a serve and still lands in the correct service box. According to the International Tennis Federation's own rulebook, as reproduced by TennisCompanion, "the service is a let if... the ball served touches the net, strap or band, and is otherwise good... In the case of a service let, that particular service shall not count, and the server shall serve again."

Two other situations trigger a let: the served ball clips the net and then hits the receiver, or anything they're wearing, before touching the ground; or the server serves before the receiver is actually ready. Outside of serving, umpires and players also call lets for genuine outside interference: a ball rolling onto the court from a neighboring match, a sudden noise or disturbance mid-point. None of it counts as a fault against either player. The point simply gets replayed, per Wikipedia's summary of the rule, which cites the ITF's official rules directly.

Why does the net make a serve replay instead of a fault?

If the ball hits the net and lands outside the correct service box, that's a fault, not a let. The let only applies when the serve would otherwise have been good. The distinction exists because a ball clipping the net cord changes trajectory unpredictably. Letting the point stand would reward or punish a player for pure chance rather than skill, so tennis has treated it as a do-over since the sport's earliest codified rules in the 19th century.

The word "let" most likely comes from the Old Saxon lettian, meaning "to hinder," the same root behind the legal phrase "without let or hindrance." A rival theory traces it to the French filet, meaning net, shortened when the English borrowed early tennis terminology. Either way, the name has outlasted several attempts to get rid of the rule it describes.

How many lets can a player serve in a row?

There's no limit. The record in professional tennis belongs to Serena Williams, who served four consecutive service lets during her 2013 win over Ayumi Morita. Chinese player Di Wu matched the feat in 2017 at a Challenger event in Anning, China. A player can, in theory, clip the net cord indefinitely and keep serving again until the ball either goes in clean or draws a fault.

Enforcement has changed more than the rule itself. In recreational play, either player can call a let, but professional tennis now relies on an electronic net sensor called Trinity, developed by German engineer Dietmar Brauer specifically to catch vibrations too subtle for an umpire to hear, the same system that overruled the video replay against Janowicz in 2016.

The rule isn't universal anymore, either. Appendix five of the ITF's official rules allows a "no-let" variant, where a serve that clips the net is simply played as it lands: no stoppage, no replay. The ATP trialed exactly that format at the 2018 Next-Gen Finals, its testing ground for rule experiments aimed at speeding up the sport. Related rule debates have played out across the tour before, which is part of why the four Grand Slams didn't share one tiebreak rule until 2022 and why the US Open never produced its own Isner-Mahut marathon. The no-let trial added unpredictability that players and broadcasters mostly disliked, and the ATP scrapped it in 2019. The let stayed — a 19th-century fix for a problem physics never stopped causing.