Aussie swim coach thrusts rail after Tokyo Olympics upset

An Australian swimming coach at the Tokyo Olympics has become an instant hit after cameras caught his wild celebrations at an athlete's golden performance this afternoon.

Dean Boxall added to the thrilling women's 400m freestyle final today after Australian Ariarne Titmus pipped American great and defending champion Katie Ledecky for the gold.

Replays showed Boxall letting loose after his swimmer touched the wall, grabbing onto nearby railing and thrusting it with his pelvis as a stunned Olympics official watched on.

"Don't try and stop Dean," a commentator said after seeing the replay.

"He is a character!"

Australian swim coach Dean Boxall reacts after the women's 400m freestyle final at the Tokyo Olympics. Source: 1 NEWS

Titmus chased down Ledecky to win one of the most anticipated races of the Summer Games, capturing the gold medal with the second-fastest time in history this afternoon.

Titmus, who trailed by nearly a full body-length at the halfway mark of the eight-lap race, turned on the speed to touch in 3 minutes, 56.69 seconds.

Ledecky was the defending Olympic champion and world-record holder. She settled for the silver this time in 3:57.36 - the fourth-fastest time ever recorded.

"I fought tooth and nail,” Ledecky said. “She definitely swam a really smart race. She was really controlled up front. I felt pretty smooth and strong going out and flipped at the 300 and it was like, ‘Oh, she’s right there.’”

And then she was gone.

For the first time in her brilliant Olympic career, Ledecky felt the sting of defeat, dished out by a rival from Down Under who made it clear she was not intimidated by the American star.

“It’s surreal,” Titmus said. “Crazy when you make this massive plan for something. It’s probably the biggest thing you could pull off in your sporting career, so I’m over the moon.”

No one else was even close. The bronze went to China’s Li Bingjie in 4:01.08.

New Zealand's 17-year-old Erika Fairweather placed eighth. 

- Associated Press contributed to this report