Base Class: Fighter
There are many who choose, when pressed by great foes to supplement themselves with magic or to come to rely on exhausting techniques. A knight does neither of these. A knight understands than an opponent who is unarmoured and unarmed does not stand a chance against true martial prowess and one who is armed need not remain so. One who commits themselves to the path of knighthood forgoes the use of magic though they need not refuse it's aid.
Keen Defender
When you choose this archetype at 3rd level, you can add half of your proficiency bonus (rounded up) to your AC. When a friendly creature of your size or smaller within 5ft of you is targeted by an attack, you may spend your reaction to swap places with that creature, making yourself the new target of the triggering attack.
Sunder
Starting at 3rd level, you have taken your first step as a knight and learned their most basic technique. As an action on your turn, you can make an attack roll against an item being carried or held by an opponent. The target adds their DEX to a number suitable for the item (Usually between 8 and 12) in order to determine the item's AC. On a successful hit, you make a contested strength check by the base number given for the item. On a success, the item is immediately sundered, on a failure, the item is damaged and will require another use of this ability to break completely. If you sunder a damaged item, you need not make the strength check.
At 10th level, you can use this feature against items which are worn as well as items being carried or held.
At 18th level, you can try to sunder a creature's natural defences. Add the creature's CON bonus to the check.
Masterful Strokes
Starting at 7th level, you have learned to strike foes through their defences magical or not. Your attacks count as magical for the purposes of overcoming resistance and immunities.
Shocking Technique
Starting at 10th level, when a creature within 5ft of you casts a spell which requires an attack roll, you can use your reaction to attempt to interrupt it. Make an attack roll against the creature. If the attack hits, that creature must make a concentration check against the full damage of that attack. On a failed save the casting is interrupted and the spell is wasted.
At 15th Level, you can use this feature against the casting of any spell which requires a saving throw, also.
Dissonance
Starting at 15th level, you have begun to separate yourself from the Weave. You gain resistance to damage from spells and advantage on saving throws against them. You can no longer be attuned to more than two magic items.
At 18th level, you can no longer attune to more than one magic item but your greater disconnect from the weave gives you resistance to damage from all magical effects and advantage on saving throws against them.
Knight Commander
You can gain expertise with one weapon type of your choice.