Nevron Kicking Incident
From AmtWiki
Re-enactment of the kicking many years later
Basically Nevron Dreadstar kicked Lief, who was a young (early teens) kid at the time, dropped his belts for a time as penance, and was eventually reinstated.
Some time after that, Ivar Nefarious made a set of collectible trading cards for amtgard knights based on the card game Magic the Gathering. The card for Nevron in this game read "summon boy-kicker". This apparently greatly angered Nevron, who was upset that his shameful act of the past was brought to light again, at a time when it seemed buried and mostly forgotten.
Some attribute Lief's fighting prowess to having been kicked in the chest by Nevron at a young age.