Way of the Pit Fighter

Unlike other monks having been trained while in a monastery, you have had your time training in pit fights. Whether the fights were upfront and honest or shady and run in secret, you have had a different kind of training. Using skills you learned from either watching other fights, or doing them yourself, you can put the hurt on anyone who stands in your way by convincing them with your fists.

Pit Grit

After having been in even more fights, you learned that you should start getting real mean for your opponents. At 6th level, you can now put the hurt with heavier punches and take the hurt from heavier punches.

When dealing damage with your martial arts die, you roll an additional d4 to add to the damage.

Additionally, when you take damage yourself you can use a reaction to roll a d4 to reduce the damage taken.

This additional die scales up like your martial arts die. (d4 at lvl 6, d6 at lvl 11, and d8 at lvl 17)

Pit Fighter's Tenacity

Your skills have grown from your days of pit fighting, you know how to use whatever advantages you have effectively.

Starting at 3rd level you add your Wisdom modifier to your initiative and have advantage on enemies that haven't already had a turn.

Additionally, at the start of your turn, you can choose to gain temporary hit points equal to the roll of your martial arts die + half your level. You can use this a number of times equal to your proficiency bonus and regain all expended uses after a long rest.

Knockout

Having been in the many tough fights you been in, you decided now is time to throw the ultimate move and go for that knockout. 

Starting and 17th level, you can decide to spend 4 Ki points to force your opponent to make a Constitution saving throw. If they fail, the opponent takes 10d10 bludgeoning damage and are knocked unconscious for 1 minute. (This attack is considered magical for overcoming resistance)

On a successful save, the target takes half damage and is stunned until the end of your next turn. While the target is unconscious, one of their allies can attempt to wake them up allowing them to roll a constitution saving throw. On a successful save, they wake up and their turn ends.

Street Tactics

From your time in the pits, you learned very quickly that not all fighters are fair and clean, using your knowledge to your advantage you decided it's time to use those tactics yourself.

Starting at 11th level, as a bonus action you can spend a Ki point to distract your target, giving it Disadvantage on attack rolls until the start of your next turn and the next attack against the distracted target has Advantage. If the target does not require vision, then they are unaffected.