Brawler

The Brawler fights in the most natural way possible:  bludgeoning their opponents over and over again with heavy, targeted punches.  Excelling in unarmed combat, the Brawler prefers straight tests of strength and will, over mindful tactics or clever schemes.

Fisticuffs

Starting when you choose this subclass at 3rd level, your skill at unarmed combat allows you to bludgeon your enemies with your fists alone.  When you make an unarmed attack to punch a creature, you add your proficiency bonus to the attack roll.  On a hit your unarmed attacks deal 1d6 bludgeoning damage, plus your Strength modifier.

In addition, whenever you use your Action to attack and you are holding nothing in your hands, you may make an additional unarmed attack as a bonus action.

Unyielding

Starting at 7th level your body and spirit have been toughened by combat.  When an enemy hits you with an attack, you may use your Reaction to reduce the incoming damage of the attack by 1d10 plus your Constitution modifier.  Alternatively, when an enemy makes an attack against you and the attack is a critical hit, you may use your Reaction to negate the effects of the critical hit.  If the resulting attack roll would still hit your armor class, you take damage from it as normal.

You may use this feature a number of times equal to your Constitution modifier, regaining expended uses following a long rest.

Haymaker

Starting at 10th level, you are able to trade accuracy for power when you strike your foes.  Whenever you make an unarmed attack against a target, you may choose to impose disadvantage on your attack before making the roll.  If the attack hits, you do not roll damage for it.  Instead, you automatically deal the maximum amount of damage possible.

Iron Fists

Starting at 15th level, your fists are like balls of solid iron.  Your unarmed attacks now deal 2d6 bludgeoning damage on a hit.  They also ignore a target's resistance to nonmagical bludgeoning damage, though your fists are not considered magical.

One-Two Punch

By 18th level you can daze an opponent with your furious fighting style.  When you strike one creature with two unarmed strikes in the same round of attacks, that creature must make a Constitution saving throw (DC = 8 + your proficiency bonus + your Strength modifier).  On a failure, the creature is dazed until the end of your next turn.  A dazed creature cannot take reactions, and can only take an action or a bonus action on its turn, not both.  Its movement speed is reduced by half, and when it takes the Attack action on its turn, it can only make one attack, ignoring any multiattack feature it has.  Finally, the creature has disadvantage on all attack rolls, ability checks, and saving throws.