Dramatic footage taken from the shore at the time showed the man’s surfboard go flying after he was bitten on his left leg.
But Frost said despite his shock, he was able to remain calm by repeating “you’re going to be all right, you’re going to survive”.
“Landed in the water and as I’ve surfaced, I’m thinking, ‘what the f–k was that?’
“When I say ‘nicked’ I’ve still got a good gash on my leg and a couple puncture wounds a bit higher, but nothing crazy, nothing like what it could’ve been.”
Frost says he decided his only option was self-defence.
“That doesn’t really do much, it didn’t even flinch,” he said.
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“But then I started punching it, in the side towards the gills, and I must have got one punch in where it’s touch sensitive and it just shot down into the depths.
“I was just saying to myself, ‘you’re going to be all right, you’re going to survive.’ Just doing what I could to try and keep calm.”
After arriving back at the beach, a nurse tried to give Frost first aid before he was rushed to hospital by ambulance.
The shark was spotted again 15 minutes after the attack, which was the seventh in WA water this year.
Doctors expect Frost to make a full recovery.
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