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.