Here's the shot, caught on a woman's cellphone at Coffs Harbour.
The shark captured by amateur photographer Steph Bellamy was estimated at around 7 feet long.
An expert from James Cook University told the Associated Press that it was possibly a spinner shark, which is common in the region and known to jump from the water.
Bellamy, 47, told the AP on Tuesday that she did not know the splash in her viewfinder was a shark until she examined the image on her phone.
"He jumped twice, he photobombed big time, then he went on his way," Bellamy said.
Here's a magnified version of the close encounter. Some in the water thought it was tuna.
Among the nearby surfers who didn't immediately realize it was shark was Lee Winkler.
"It was having a bit of fun," Winkler told the AP. "It just jumped up and had a spin, then jumped up and had another spin, then went away."
After Bellamy showed the image to event organizers, the surfers were called out of the water, only to return about 15 minutes later to finish the competition.