Dropping in on another surfer's wave is the laid-back sport's greatest crime.
So when a Brazilian gatecrashed Kiwi Tim Thompson's ride on three straight barrels, he decided to do something about it.
In a video that has gone viral, Mr Thompson is seen rugby tackling the contemptuous Brazilian and wiping him out.
"Let's just say my exit off the wave was either poorly timed or perfectly executed, depending on how you look at the situation," Mr Thompson wrote on gosurf.co.nz which first posted the video.
The incident happened during a trip to the Mentawai Islands off Sumatra last month.
And the video has earned Mr Thompson widespread praise in the surfing community.
Mr Thompson told Wide World of Sports told how the incident came to a head.
"I don't want to encourage this at all, I am a very mellow guy in the surf and this is not at all how I normally would act," he said in an email.
"However, due to the circumstances and my mood at the time it did seem like a fitting act."