TL;DR: It seems every pro athlete has a signature victory dance or emote. Those that don't might borrow from others or even video games. Apparently, tennis champion Daniil Medvedev is a big FIFA fan, as he demonstrated the Dead Fish celebration after winning the US Open this weekend.
Russian tennis champ Daniil Medvedev won the US Open on Sunday by beating number one ranked Novak Djokovic in an upset victory. To celebrate, Medvedev did something that somewhat puzzled the crowd. He dropped to the court and played dead. Afterward, he explained what he did, but it only confused them more.
"Only legends will understand what I did after the match is L2 plus left," said Medvedev before leaving the court.
What he was referring to is a FIFA post-goal celebration. A few years ago, EA added celebrations to FIFA. Players execute them with specific button combinations. Holding the L2 trigger while pushing left on the right joystick performs the "Dead Fish" or "Brick Fall" on the PlayStation version (below).
Medvedev did not execute it properly, as players (and the game animation) jump into the air before falling to the turf. However, on the hard surface of the US Open, a proper Dead Fish might have resulted in injury. Even had he done it correctly, it's doubtful the tennis crowd would have recognized the move. The announcers just thought he was tired. In addition to being the first pro tennis player to perform a FIFA celebration on the court, Medvedev's Sunday victory earned him a couple of other accolades.
His win made him the first Russian to win the US Open since Marat Safin beat Pete Sampras in 2000. Medvedev also prevented Djokovic from becoming the second man in the Open Era to achieve a calendar Grand Slam in men's singles since Rod Laver pulled off a sweep in 1969. A calendar Grand Slam is winning all four majors in a calendar year---Australian Open, French Open, Wimbledon, and US Open.