The ollie FS180 combines a flat-water ollie with a frontside 180 rotation: pop off the tail, spin 180, and land switch. It's the first time you're spinning purely off your own pop - no kicker, no obstacle.
The skill it tests is initiating the rotation as you leave the water, not after you're already in the air. Pop first, spin second - but barely. If you wind up on the water you lose the pop; if you wait until you're airborne you under-rotate. Confident switch riding makes or breaks the landing.
See more here (translated audio but good tips):
Video by WakeboomerTV
Key tips
- Get a clean flat-water ollie down first. This adds rotation on top
- Initiate the rotation as you pop, not after you're in the air
- Spot the landing by looking over your shoulder through the spin
- Land with knees bent and ride away switch
- Confident switch riding is what saves the landing - drill it first
- Practice in both regular and switch stances (the switch version is a surface BS180 with pop)