Doug Niblack was surfing in the coastal city of Seaside in Oregon on October 10 when he was apparently hit by the shark, said to be at least 10 feet long.
The shark reportedly dragged the surfboard with its dorsal fin before taking off several seconds later, according to KATU.
Niblack then swam as quickly as he could until he reached the shore.
"It pulled my leg about three feet, hooked on my leash, then it was gone," he recalled. "And that was the scariest part, when I didn't know where it was anymore."
Fellow surfer Jake Marks, who was near the incident, backed up Niblack's story - even though he never saw the shark itself. He said: "I have no reason to doubt there was a shark out there.
"With the damage to his board, the way he was yelling and trembling afterwards, there is no other explanation for that."
Marks joined Niblack in hastily making for safety after Niblack warned him of the shark's presence.
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