Generally speaking: if he behaved "in a way unbecoming a Christian knight". That might vary from running away in battle, ravishing or killing a defenceless women (although that should read as 'noblewoman') to betraying the trust in any other way of his liege lord. Truth be told, it didn't happen very often.
A knight could be stripped of their knighthood by committing serious crimes, engaging in dishonorable conduct, or failing to uphold the chivalric code of honor. This could result in the individual being formally removed from the order of knighthood by the monarch or governing body responsible for bestowing such titles.
A dishonored knight might face consequences such as loss of rank and titles, ostracism from the knighthood community, and a damaged reputation that can be difficult to repair. In extreme cases, the knight may be banished or stripped of their knighthood altogether.
Criminal Activity and Moral Turpitude can all lead to a revocation of one's knighthood. Sir Anthony Blunt was stripped of his Knighthood. Obviously spying for the Russians is frowned upon !
The three stages of knighthood were page, squire and knight.
page, squire, knight
page, squire, knight
it can be Ritterschaft "ritter" is knight "schaft" is community
First you are squires assistant Then squire Then knight
page, squire, knight
A knight would often be a vassal of a more powerful noble, or subsidiary to the noble in another way.A powerful noble could also hold a knighthood himself.
Knighthood was usually not hereditary. This meant that technically, anyone could be made a knight. Usually, the people who trained for knighthood were sons of noble families, and so most knights were members of the nobility, but there were exceptions. Some people were not trained to be knights, but were simply given knighthood as an honor because of some great deed, and in such cases the relatives could be anyone from kings to peasants. There is a record of a very large number of otherwise ordinary women being given knighthood after they fought in a battle in Catalonia. They were made members of an order created for them, called the Order of the Hatchet.
He was charged with "treason" for betraying the order of knighthood.
king, kingdom, knight, knighthood, ...