In what ways could an ordinary free man become dependent on the nobility?

A free person could, for example, be captured during hostilities, and be sold into slavery. The enslavement of a free personality could also occur if the peasant fell into debt bondage due to the impossibility of returning the grain or implements borrowed for sowing to the landowner, so the owner could sell it on the market or force him to cultivate his fields free of charge. If European knights were hired to serve a noble feudal lord, then they also lost their freedom to a certain extent, becoming vassals.