Your natural desire to lead the party, whether out of selflessness or pride, have lead you to take on most encounters head on. As such, you've learned that taking a few hits is only natural, but worth defending those behind you. After gaining the experience and skills to adapt to the frontlines, you've began to master a more defensive, yet threatening, fighting style, one that incorporates counters, deflections, and tactical survivability.

Level 3: Predictable Blows

You've been hit enough times to see where this is going. As an action, take a defensive stance. If a creature enters the range of your melee weapon, you may use a reaction to make an attack against them with advantage. On a hit, the creature's movement becomes 0 until the start of their next turn. On a miss, creatures gain advantage on attacks against you until the start of your next turn..

Level 3: Hunker Down

Stand your ground and let them come. As an action, gain AC equal to your STR+CON modifiers until the start of your next turn. Any attack rolls made against you have advantage, including grapple checks. This can be done a number of times equal to your CON modifier plus your proficiency bonus, and you regain expended uses on a short or long rest.

Level 7: Counter Cuts

Teach them a thing or two about combat. As a reaction, you may target a creature making an attack roll on you and invoke disadvantage. If the attack misses, you may make an attack against them with advantage. This ability can be used a number of times equal to your STR modifier plus your proficiency bonus, and you replenish uses on a short or long rest.

Level 10: Hold The Line

They shall not pass. When you make a successful attack against a creature, you may use a bonus action to select the target and 1 additional adjacent creature and reduce their movement by 20 feet until the start of their next turn. Any opportunity attacks provoked by these creatures gains advantage.

Level 15: Critical Cleaves

There's more of them, but that only makes it even. Whenever you score a critical hit on a creature, you may also attack an adjacent creature with advantage. You may use this feature a number of times equal to your STR modifier plus your proficiency bonus, with uses replenished on a short or long rest.

Level 18: The Best Defense

Enough is enough, why wait for them to strike first? As a free action, enter an enhanced combat state. In this state, gain additional attacks and AC equal to your proficiency bonus. Attacks made against you gain advantage, but your opportunity attacks to not expend a reaction, and can be used whenever you would trigger opportunity attacks. This state lasts until you end your turn without dealing or receiving damage, but may be canceled upon becoming unconscious to gain hp equal to your max hit dice plus your fighter level, gaining a point of exhaustion after combat ends. Can be used again after a long rest.