Mark McCracken was fishing off the coast of Santa Barbara, California, on Saturday when a hammerhead shark began circling his kayak.
McCracken, 33, posted video of the encounter to Instagram, writing that he was fishing for bonito when a "tweaked out hammerhead started ramming and biting my kayak."
In the video, the shark is visible — often by its distinctive dorsal fin — circling and darting toward the kayak as McCracken jabs into the water with his paddle. He appears to repeatedly make contact with the shark's head and body.
"I had to hit him over 20 times before he finally gave me some space but still stalked me for a half mile all the way back to shore," McCracken wrote on Instagram.
In an extended version of the video posted by NBC News, McCracken says he is "pretty sure I just kicked a hammerhead's ass. I just beat up a shark."
The encounter lasted about 15 minutes, NBC New reported.
He added on Instagram that even after returning to shore, the shark continued to swim "in about 3 feet of water like he was just waiting for me to come back out."
BuzzFeed News has reached out to McCracken for comment.
McCracken's battle is at least the second significant encounter between a hammerhead shark and a human near California this summer. In August, a man was diving about 100 miles from San Diego when a hammerhead bit him on the hand.
Hammerheads normally live in tropical zones, but have recently been drawn north to California as a growing El Niño leads to warmer-than-usual waters.