Jeff Horton was surfing Sunday morning with about 10 others near Kilauea when someone spotted a fin in the water, a local newspaper reported.
Twenty minutes later, Horton was sitting on his surfboard with his legs dangling in the water when he spotted a dark shape approaching from the left. He thought it was a stingray - dark on top, white on the bottom.
"It came flying straight toward me," he said.
He pulled his left leg out of the water and the shark got a mouth full of surfboard.
The impact knocked Horton off the board. He rolled onto the shark and grabbed a fin.
On top of the shark, holding on with one hand, he began punching as hard as he could with his other fist. He estimated he landed eight blows.
"I finally got one nice punch into the eye," Horton said. "I put some really good hits on it, for sure."
When his knuckled jammed into the shark's eye, the shark spit out the board and retreated.
Horton scrambled onto his board. With another surfer, he caught a wave and paddled toward shore.
The shark briefly followed but did not attack again, he said.
After they reached shore, a tourist gave him $50 and told him to buy a bottle. Horton's only injuries were scratches from the shark's rough skin.
The 7-foot board, however, was left with a semi-circle imprint of the shark's jaws.
It will not go back in the water.
"I'm going to put it up on my wall," Horton said.
He surfed again Monday at another beach.