The foil climbs too high, the front wing breaks the surface and pulls air instead of water — lift collapses in an instant and the board slams back down.
Overfoiling is the mirror image of a touchdown: not too little height, but too much. The moment the front wing breaks the surface, air flows along it, lift vanishes in a fraction of a second and you land hard. It's usually triggered by speed outrunning the wing's size, or by the reflex to lean back as soon as things get twitchy. The correct response is unspectacular: deliberately reduce angle of attack or speed rather than fighting it — reflexive corrections only amplify the porpoising. And look at the horizon, not at the nose. What often gets missed: not every sudden loss of lift is overfoiling. There is also ventilation, where air is drawn down along the mast and disturbs the flow even though the wing stays submerged. The remedies differ, which is exactly why it pays to tell the two apart.