Path of the Pugilist

No, like seriously, he punched a hole through that guy's chest! With one punch!

- Carren Morzil, sole survivor of the brawl

Barbarians are often feared for their ferocity and strength, destroying their foes' defenses with their powerful swings and potent strikes, but those can be easily quelled by simply removing their weapons, then they become significantly easier to deal with. Unless they're a Pugilist.

While monks focus their inner reserves of energy, ki, and focus on damaging their foes' weak spots and disrupting them, a Pugilist knows such training is pointless when you can break a good percentage of bones in a body with a single punch. Those who walk the Path of the Pugilist learn to adapt and overcome, not with clever thinking, but with clever punching.

Raw Power

Starting when you choose this path at 3rd level, you learn to put your entire strength behind your fist.

When you take the attack action on your turn while raging and make at least one Unarmed Srike, you can make a single Unarmed Strike as a bonus action.

When you hit with an unarmed strike, you can roll 1d4 in place of the normal damage of an Unarmed Strike, and add your Strength modifier to the damage roll. 

This die increases when you reach certain levels in this class, increasing to 1d6 at 6th level, 1d8 at 10th level, 1d10 at 14th level, and 1d12 at 18th level.

Brace

Starting at 3rd level, you know not only how to dish out a hit, you know how to take one too.

When you take damage from a source that you can see and are not surprised by, and you are not wielding a weapon or a shield, you can use your reaction to reduce the damage you take. The reduction equals a roll of your Raw Power die + your Constitution modifier (minimum of 0). You can use this reaction a number of times equal to your Proficiency bonus, regaining all expended uses at the end of a short or long rest.

If an attack or effect deals multiple damage types, you choose which damage is reduced. If a damage type is reduced to 0, any remainder reduction is carried over to another damage type.

Reversal

Starting at 6th level, your reflexes have heightened to the point that you can react to even the fastest attacks.

If a creature hits you with a weapon attack while within 5 feet of you, and you reduce the weapon damage to 0 using your Brace ability, you can make a single unarmed strike as part of the same reaction. If this attack hits, you can force the creature to make a Strength saving throw (DC equal to 8 + your Strength modifier + your proficiency bonus), dropping whatever it is holding on a failure.

Rule Tip: Weapon Damage

Weapon Damage refers to the damage of the weapon before any enchantment or additional effects are added, any damage that is referred to as extra or bonus damage is not part of the Weapon Damage. For example, a Flame Tongue short sword's weapon damage is 1d6, while the 2d6 fire damage is bonus damage. Spells and magical effects behave in a similar way, for example the 1d6 necrotic damage granted by Hex is bonus damage.

The additional damage from a critical hit is not extra damage and is included in the Weapon Damage. Depending on the wording, this may appear as an exception to this rule.

Breaking Force

Starting at 10th level, your fists hit with enough force that they can even break through magic, completely destroying it.

Once per turn, when you hit a creature or an object with an attack, you can attempt to end one magical effect affecting it. You can roll your Raw Power die. If you roll a number equal to or higher than the level of the spell on the die, the spell ends. Since you are attacking the magic directly, you can choose to have this attack deal no damage to the creature or object.

Alternatively, you can use your action to target a spell effect within 5 feet of you and attempt to disrupt it, making the roll the same as above.

You can use this feature a number of times equal to your Proficiency bonus, regaining expended uses at the end of a long rest.

Adrenaline

Starting at 14th level, your pure strength that can break magic and bones, can also break your injuries, but in a good way.

While you are Raging, you can use your bonus action to send a surge of adrenaline through your body, repairing it slightly. You regain hit points equal to your Raw Power die + your Constitution modifier (minimum of 0) if you have fewer than half of your hit points remaining.

Arcane Parry

Starting at 14th level, you have learned to combine your bracing ability and your magic-shattering strength.

When you are targeted by, or included in the area of, a spell or magical effect and aren't surprised, you can use your reaction to expend a use of your Breaking Force ability to attempt to disrupt and counter the spell. You roll your Raw Power die. If you roll a number that is equal to or higher than the level of the spell, the spell fails and has no effect.

Change Log

2.2 - Changed Brace uses to scale with Proficiency. This allows Barbarians to prioritise other improvements when they get their ability score improvement, instead of dumping everything into Con, though its effectiveness is still based on Con.
Restricted Raw Power's bonus action attack to only while raging. This slightly reduces the power of the ability but moves it back onto Rage, which I felt the subclass was slightly overlooking in some ways.
Restricted Raw Power's bonus action attack to after making an Unarmed Strike attack. This is solely to put some more emphasis on the Unarmed Strike aspect of the subclass, otherwise using any other weapon would be more effective at lower levels, losing some of the intent of the subclass.
Changed Breaking Force and Arcane Parry from a Strength check to a flat roll using Raw Power die. Strength checks for Barbarians are child's play, especially while raging, thus this change is intended to make it slightly more difficult to overpower the higher level spells, though easier to overpower the lower level spells.
Breaking Force and Arcane Parry now share a use pool. With the above changes, Breaking Force is now significantly more powerful, especially when targeting lower level spells, so this change is intended to limit both it and Arcane Parry, so that it doesn't find itself used every turn.

2.1 - Minor D&D Beyond character sheet formatting adjustments.
Clarification of rules, added a Rule Tip to Reversal.
Changed Brace to restore uses at the end of a short rest.
Changed Adrenaline to be a bonus action activated heal that scales with Raw Power. The intent of this change is to make the increases granted by Raw Power feel even more important and to give the subclass more decisions to make, whether they use their bonus action for the extra damage or for a heal.

2.0 - Removed Bone Breaker, replaced 6th level ability with Reversal. The intent of this change is to make the subclass feel more martial, something more than just punching and taking punches.
Removed Advantage on Constitution saving throws from Adrenaline. Found to be mostly redundant and made the ability slightly overcharged.
Added Arcane Parry. Again, the intent of this is to move the subclass away from the simplistic 'hit and be hit' mindset Barbarians often fall into, granting a little more versatility and the ability to (sort of) support their allies.
Increased base DC for Strength check for Breaking Force and Arcane Parry from 12 to 13. Simply to make it slightly more difficult to consistently succeed on a somewhat powerful ability.
Added the ability to make an unarmed strike as a bonus action as part of Raw Power. This is to support lower level Pugilists, as the unarmed strike focus makes this subclass significantly weaker than other subclasses in the damage department especially in early levels.