Knights had no compunction against fighting on foot. They dismounted when necessary, and fought mounted when that was more advantageous. At Tinchebray in 1106 and at the Battle of the Standard in 1138 Anglo-Norman knights largely dismounted to fight on foot, with some remaining mounted and in reserve. At the Battle of Dorylaeum, and in other clashes during the First Crusade, Frankish knights fought on foot, at least partially due to a critical shortage of horses, many of whom had died. Throughout the Hundred Years' War, most knights, or to name them properly, men-at-arms (actual knights were fairly rare by the 14th century, being heavily supplemented by less prestigious chaps called variously esquires, armigers, etc, who fulfilled the same role) fought on foot.

Further, there is no reason to assume that an armored person is necessarily a knight or a horseman. Semi-professional infantry was widely used throughout the Middle Ages, and many of them would have had at least some metal armor. It likely would not have been as modern or as extensive as that used by a warrior aristocrat, but the high school image of medieval armies as being composed of a tiny core of elite knights and a vast levy of half-naked peasants is laughably wrong. Mercenaries, especially after 1100, were hugely popular, and hardly a campaign was waged without some of these bands along.