A variant on the standard wedgie when the waistband of the victim's underpants is pulled up so high, he has no alternative but to flip forward as he who executes the maneuver gives a 'helping push' in order to to encourage the best possible flip (the victim ideally completing a full roll after hitting the ground). The simultaneous pulling on the band of the underpants while pushing the victim forward is said to resemble a "hook"-like motion.
The "Pumpkin Hook" takes its name from the hamlet known as Pumpkin Hook in Farmington, NY (western Finger Lakes region of NY state; Ontario County). It is here whence maneuver originated and has been practiced, at least under this name.
1) No no, this wasn't just a run-of-the-mill wedgie...they gave that poor botard a full-blown Pumpkin Hook right there in front of the school while all the buses were loading. I felt pretty bad for the S.O.B.
2) It was all fun and games until he Pumpkin-Hooked his buddy and things turned ugly pretty fast.