Dirty Brawler

A dirty brawler, as the name suggests, is an individual who is not bound by combat morality or codes of honor during engagement. Though they can be good at heart, they can also turn out to be horrid murderers with intense calculation upon deciding to fight their foes, or brutalize them. Typically revered as psychopaths.

These individuals do not dominate the space of a city and are quite rare due to their unique mixture of advanced tactics and street knowledge.
However, these people, if exposed to groups, tend to climb the ranks of a martial system quite quickly given they aren't killed off before they get a chance to prosper.

Brutalist

You have mastered the art of survival. If you kill the thing before they kill you then you survive.
Starting at third level, you become proficient with Improvised weaponry, them always doing 1d4+STR modifier unless instructed otherwise by the DM.
You also become gain the 'Tavern Brawler' feat, allowing you to do increased damage with your fists without being proficient in martial arts.

Devious Mentality

At 7th level, your mentality has heavily degraded over the time that you have been desensitized to fear. When examining recently dead corpses, you gain advantages on all wisdom rolls to find the cause of death or finding loot amongst them.

Backup Bash

At 10th level, you gain the ability to make an unarmed attack at no action twice per short rest. This attack can be made against any creature within your unarmed attack range. If they are hit with this attack, they gain disadvantage on all attacks for 1d4 turns.

Filthy Moveset

At level 15, you become quite the powerhouse when it comes to dirty ways to hit your opponent. Immediately after you take the Attack action on your turn, you can make two unarmed strikes as a bonus action 5 times per short rest. You also gain advantage on athletics checks and strength saves.

Unkillable Energy

Finishing off at 18th level, you have become used to being beaten around and have become really hard to kill by non-magical means. You gain resistance to all non-magical physical damage. You also gain advantage on death saving throws.