6 February 2017 Last updated at 09:46 GMT
British player Kyle Edmund was beating Denis Shapovalov from Canada, when frustration got the better of him.
The 17-year-old Canadian whacked the tennis ball in anger, only to hit the umpire in the eye!
As a result the match could no longer continue, meaning Great Britain won by default.
Kyle will now go on to face off against France in April.
Shapovalov apologised to the umpire after the match, and his coach hopes he will learn a lesson from it.

The 18 sketches are by artist Donald McGill who produced more than 12,000 original artworks for the postcard industry between 1904 and 1962.
Along with a pun-filled caption, the pencil sketches include stamped approval by the censorship board.
They sold for between £55 and £220 and fetched about £1,200 in total, auctioneers Moore Allen said.
Described as the "king of the saucy postcard", McGill produced thousands of artworks and an estimated 200 million postcards were printed and sold.
Often with a double, risqué meaning, one of his sketches shows a buxom blonde flashing her bloomers as she waters a flowerbed with a passing man saying: "I like her display of pinks, Fred!"
Another features a red-faced policeman telling a curvy blonde driver with a broken taillight: "You've got no light behind, so I'm afraid I'll have to pinch you."
But in the 1950s, McGill fell foul of a crackdown on the saucy postcard industry and was prosecuted and fined under the 1857 Obscene Publications Act.
Many postcards were destroyed by their owners during the government crackdown.

The bag rocks alarmingly from side-to-side and threatens to overturn.
Now, scientists have investigated this conundrum of everyday physics. Speeding up rather than slowing down can solve the problem, they say.
Alternatively, you can pivot the handle of the suitcase as close to the ground as possible.
French scientists studied a model suitcase on a treadmill to see what goes wrong when a suitcase rocks out of control at high speed.  They developed equations to explain why two-wheeled trolleys have a tendency to rock from one wheel to the other.
In cases of unstable bags - after having gone over a bump, for example - they found luggage rocks from side-to-side until it falls over, or it reaches a regular side-to-side swing.
If a regular side-to-side swing develops, going faster results in smaller swings, said the researchers.
"Thus, one should accelerate rather than decelerate to attenuate the amplitude of oscillations," they explained.
"A non-experienced suitcase puller would not react this way. The outcome should not be a dramatic for a suitcase, but it could be troublesome for a trailer towed by a vehicle."
This leads on to important practical implications of the research, which is published in the journal HRoyal Society Proceedings A.
"The suitcase is a fun way to tackle the problem but the study would be the same for any trolley with two wheels or blades," Sylvain Courrech du Pont, of Universite Paris-Diderot, who led the study, told BBC News.
"So it will be the same for a caravan or maybe also for airplanes."
In technical terms, the mechanical instability is mainly due to the fact that there is a coupling between the translational motion and the rotational motion of the suitcase.
It comes about because the two wheels are fixed together on a rod.
In April, scientists solved another problem of everyday physics - why shoe laces come undone.
They found the force of a foot striking the ground stretches and then relaxes the knot, while a second force caused by the leg swinging acts on the ends of the laces, like an invisible hand.
This too has practical applications for structures such as DNA.
Follow Helen on HTwitter.
Great Britain are through to the Davis Cup quarter-finals, after a Canadian player accidentally hit the umpire with a tennis ball.
[NEXT_CONCEPT]
Original bawdy sketches the basis of thousands of "saucy seaside" postcards have been auctioned in Gloucestershire.
[NEXT_CONCEPT]
It's a common experience when dashing for a train or plane while lugging a two-wheeled suitcase.