Path of The Iron Fist

Some Barbarians embrace the heat of battle to such a degree that simply grabbing a weapon is but a waste of time to them, choosing instead to fight with their fists, legs, and teeth.
Unarmed Barbarian subclass.

Unarmed Combatant

At third level, when you choose this path, you gain the following two effects:

• Any time you score a critical hit with an unarmed attack, you can choose to roll one hit die to restore hit points equal to the rolled number + your constitution modifier. If you are out of hit dice you instead restore hit points equal to just your constitution modifier. 
  
  
• Your unarmed strikes now do 1d6 + your strength modifier bludgeoning damage. If your DM allows, your fists now count as simple weapons.

You In Particular

Starting at third level, whenever you enter a rage, you set your sights on one enemy in particular whom you desire to take down. When you do so, you gain a burst of movement equal to half your movement rounded down straight towards the enemy. If you make it within range of the enemy you may make one unarmed strike as a reaction. (This is not affected by "One-Two-Combo").

If you hit your designated foe with this attack, they will have disadvantage on their next attack roll or saving throw.

One-Two-Combo

At sixth level, when you rage, you gain the ability to follow up your successful attacks with a swift unarmed strike from your offhand as a bonus action, this attack does 1d4 damage + your strength modifier.

Additionally, your experience in hand to hand combat allows you to exploit an enemy's weakness to strike true. Whenever an enemy is prone, or you have advantage on them, you do increased damage. Your regular attacks increase from 1d6 to 1d8 and your One-Two-Combo attack increases from 1d4 to 1d6.

Fighting Stance

At 10th level your dedicated training has paid off and you unlock a pool of Martial Points equal to your strength modifier + half your proficiency rounded down (minimum of one).
Martial Points recharge after every long rest, and can be used to swap between several Martial Stances, Stances reset to Neutral Stance after fulfilling their purpose:

• Aggressive Stance (1 point): As a bonus action, enter an aggressive stance to grant yourself advantage on your first attack against an enemy.
• Defensive Stance (3 points): As a reaction when you get hit by an attack, raise your guard to increase your AC against that attack by half your strength modifier + your proficiency bonus. 
• Evasive Stance (2 points): As a bonus action when you are not raging, enter an evasive stance, dropping your speed to zero and reducing the incoming damage of all ranged and area of effect attacks by half until the start of your next turn.
• Protective Stance (3 points): As a reaction when an enemy hits an ally you can see, that is within half your movement, you expend up to half your movement to interpose yourself between the attacker and the ally, instead causing the attack to contest with your AC. (If there is no space in-between the attacker and your ally, you shove your ally 5 feet behind you to take their place).
• Agile Stance (1 point): As a bonus action, you enter an agile stance which allows you to move an additional 10 feet.

Eye of The Tiger

At 14th level, your single-minded determination to bring down your adversaries manifests itself in your physicality, and your strength transcends that of mere mortals. You gain the following effects:

• Your unarmed strikes now count as magical for the sake of overcoming resistances and immunities.
• Your unarmed strikes has their damage increased by an additional damage die (Attacks do 1d8 and One-Two-Combo does 1d6 and the empowered versions do 1d10 and 1d8 respectively).
• You gain the ability to let out a mighty roar that affects anyone within 60 feet of you whenever you roll initiative, causing anyone who fails a wisdom save to take a -2 penalty to their initiative roll. The DC is equal to 8 + your strength modifier.
• When you critically strike or defeat a creature, you gain temporary hit points for one minute equal to your constitution modifier + half your barbarian level. (Additional temporary hit points are not added on top of existing ones but simply replaces them).
• You gain expertise in intimidation and can choose to add your strength modifier instead of your charisma modifier. You have advantage on substituted intimidation checks while raging.