Praetorian Guard

Devoted Defender

When you choose this archetype at 3rd level, you train relentlessly with defensive techniques. While you are wearing heavy armor, you gain a +1 bonus to AC.

Harm's Way

At 3rd level, you are willing to risk your own safety for that of your allies. When another creature within 5 feet of you is targeted by a melee weapon attack, you can use your reaction to switch places with the target. You become the target of the triggering attack. You must make this decision before the attack roll is made.

Retribution Strike

Starting at 7th level, you can punish your enemies for injuring your allies. If another creature friendly to you is damaged by a hostile creature, you can make a special melee weapon attack against the hostile creature as a bonus action on your next turn. You have advantage on the attack roll, and if it hits, the attack's weapon deals extra damage to the target equal to half your fighter level (rounded down).
You can use this feature a number of times equal to your Strength modifier (minimum of once), and you regain all expended uses of it when you finish a long rest.

Defensive Strike

At 10th level, you learn to interrupt an attack with a strike of your own. If a creature within your reach makes a weapon attack and you're wielding a melee weapon, you can use your reaction to make a melee weapon attack against the triggering creature. If your attack hits, the triggering attack has disadvantage.

Total Defense

Starting at 15th level, if you take the Dodge action on your turn, each creature of your choice within 5 feet of you gains a +2 bonus to AC until the start of your next turn. A creature loses this bonus when it is no longer within 5 feet of you. A creature with this bonus to AC also has resistance to the damage of the first attack that hits it before the start of your next turn.

Vigilant Guardian

Starting at 18th level, you can respond to danger with extraordinary vigilance. In combat, you get a special reaction that you can take once on every creature's turn, except your turn. You can use this special reaction only to impose disadvantage on an attack roll as long as you are within 5 feet of the target and wielding a shield.