A Hammerhead as described by the Book of the Golden Orb is, "The pounding of one's fist iniside another person's fishing net using the same motion as you would perform a Salmon, much like a hammerhead shark."
As one sneaks up behind a "fisherman," they should have their hands balled up into fists. As they move in, they insert their fist, and hit their fist forcefully on the inside of the fisherman's ribcage and their elbow about 10-20 times. As to comply with the Rules of Salmoning, one must say "hammerhead" as they are Hammerheading the fisherman. Then they remove their fist and proceed with daily life.