The crowd is silent in the amphitheater. Ten rounds of the tournament have come and gone, leaving but two combatants. Across the ring a massive brute of a man hefts a greataxe and glowers. No one to this point had been able to cope with the brutal ferocity of this opponent, but physical strength can only take you so far. The slender blade of a rapier hisses from its well worn scabbard and assumes a familiar stance, urging the brute forward. The bell rings. The barbarian rushes across the arena with a savage strike, but only a fool would stand there to receive it. The duelist dodges nimbly to one side and paints a red line down the brute's forearm. Again and again, the barbarian crashes his axe where the duelist had stood but a second before as more and more fine red lines appear on his arms, his legs, his chest. A furious bellow fuels one last attack, but the thin blade deflects the greataxe with consummate skill...

Absolute precision. 

The audience is silent for three seconds as the duelist withdraws the rapier from his opponent's chest before erupting into wild applause.

 

Weapon Focus

By level 3, you have begun to train with a given weapon type above others. Choose one weapon group from the list below; you gain a bonus to hit equal to half your proficiency bonus when using that weapon type.

The weapon  types are:

Swords (dagger, sickle, shortsword, scimitar, rapier, longsword, greatsword)
Axes (handaxe, battleaxe, greataxe)
Blunt (clubs, greatclub, mace, morningstar, light hammer, warhammer, maul, flail)
Polearm (spear, quarterstaff, pike, halberd, glaive)
Ranged (short bow, longbow, hand crossbow, light crossbow, heavy crossbow)
Special (whip, trident, war pick, lance)

Master at Arms

When you reach lvl7, you can spend one hour training a number of humanoids up to your charisma modifier (minimum of 1). These humanoids gain proficiency in weapons of your chosen Weapon Focus for the next 8hrs. If a humanoid is already proficient in one of these weapons, that creature can add half your proficiency bonus to their damage rolls using that weapon for the next 8hrs. You also gain this bonus.

This hour of training does not count as light activity for the purposes of a short or long rest.

Weapon Specialization

By level 10, you have mastered your chosen weapon type and gain additional benefits when using them, outlined below:

Axes

While attacking with an axe, whenever a damage die is rolled for the maximum amount, you can roll that die again and add the new roll to the damage dealt. This effect can trigger multiple times.

Blunt

While attacking with a blunt weapon, the target takes half damage on a miss, provided your roll is no more than your STR modifier less than the targets AC

Polearm

While wielding a Polearm, your attacks cleave to up to one additional target, provided they are in the attack range of your weapon and the attack roll meets or exceeds their armor class. Targets of the cleave take half the damage sustained by your main target.

Ranged

While wielding a ranged weapon, when a hostile creature moves 10 or more feet while inside your range, and you don't have disadvantage, you can use your reaction to make one weapon attack against that creature.

Special

Trident: the first time you hit a creature with your trident on your turn, the targets speed is halved until the start of your next turn. If you hit a creature with an attack of opportunity, that creatures speed becomes zero.
Whips: when you critically hit with a whip, your target is knocked prone if it is large or smaller.
War pick: while attacking with a war pick, your weapon focus feature allows you to gain a bonus to hit equal to your full proficiency bonus instead of half.
Lance: You no longer attack at disadvantage if your target is within 5ft of you. If you move at least 20ft in a straight line before making your attack, you deal an additional 10 piercing damage if the attack hits.

Swords

When you critically hit while wielding a sword, your target takes additional slashing damage at the start of its next turn. This damage is equal to half the damage of the critical hit taken.

Improved Fighting Style

At lvl15, you gain additional benefits from the fighting style you chose at lvl1. If there are any restrictions imposed by a fighting style, they must be met to gain the benefit outlined below.

Defense. You do not suffer additional damage when you are the target of a critical hit.
Dueling. Your attacks now critically hit on a roll of 19-20
Archery. You can now use your Bonus Action to grant yourself advantage on ranged weapon attacks until the start of your next turn.
Two weapon fighting. When you are two weapon fighting, you may now make two attacks with your off-hand weapon when you use your bonus action.
Great weapon fighting. When you critically strike your target, it is knocked prone if it is huge or smaller.
Protection. You can now use your reaction to shout a warning, imposing disadvantage on any attack roll targeting an ally within 30ft of you. If the attack hits, the ally has resistance to that attacks damage.

Press the Advantage

At lvl18, when you critically hit an enemy, you may immediately make one additional weapon attack against that creature. This may only occur once per round.