Beginning at 3rd level, you can use your bonus action while wielding a shield to take on a defensive stance. For the next minute, allied creatures gain half cover while within 10ft of you. 

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses of it when you finish a short or long rest.

Starting at 3rd level, you can menace your foes, foiling their attacks and punishing them for harming others. When you hit a creature with a melee weapon attack, you can mark the creature until the end of your next turn. This effect ends early if you are incapacitated or you die, or if someone else marks the creature.

While it is within 10 feet of you, a creature marked by you has disadvantage on any attack roll that doesn’t target you.

In addition, if a creature marked by you deals damage to anyone other than you, you can make a special melee weapon attack against the marked 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.

At 7th level, you learn to fend off strikes directed at you, or other creatures nearby. If you or a creature you can see within 5 feet of you is hit by an attack, you can roll 1d8 as a reaction if you’re wielding a melee weapon or a shield. Roll the die, and add the number rolled to the target’s AC against that attack. If the attack still hits, the target has resistance against the attack’s damage.

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses of it when you finish a long rest.

At 10th level, you become a master of locking down your enemies. Creatures provoke an opportunity attack from you when they move 5 feet or more while within your reach, and if you hit a creature with an opportunity attack, the target’s speed is reduced to 0 until the end of the current turn.

When you reach 15th level, your shield wall provides three-quarters cover instead of half cover and all shields you wear grant an additional +1 armor class.

If any creature benefiting from your shield wall passes a Dexterity saving throw, they take no damage rather than half damage.

Starting at 18th level, you respond to danger with extraordinary vigilance. In combat, you get a special reaction that you can take once on every creature’s turn. You can use this special reaction only to make an opportunity attack.