I remember a story about a physically strong medieval figure, I believe maybe in Normandy, who swore fealty to some relatively weak overlord, but during the ceremony kicked or knocked the overlord off his throne. The story may be apocryphal but was widespread. What incident am I thinking of? I have not been able to search for it via other means.
Perhaps you're talking about Rollo, while swearing feudal allegiance to the King Charles II of France with the Treaty of Saint-Clair-sur-Epte (911):
"According to legend, when required to kiss the foot of King Charles, as a condition of the treaty, he refused to perform so great a humiliation, and when Charles extended his foot to Rollo, Rollo ordered one of his warriors to do so in his place. His warrior then lifted Charles' foot up to his mouth causing the king to fall to the ground." (Holden, A.J. (1970). Le Roman de Rou de Wace. Paris: Éditions A.J. Picard. p.54. Lines 1147-1156)