Retiarius

The man hobbled along the cobbled street, his bunions hurting, his cheap leather and cloth guard armor itching. He stares longingly at the greatsword in the shop window that he used to own, but pawned to cover his gambling debts. Sighing he pulls his trident from his back, his other hand grabbing at the net strung to his belt. He'd seen a shadow in the shop windows reflection, sneaking up behind him. He hears the sound of a blade pulling quickly from its sheath. He ducks to the left, kicking off the shopfront and tumbles into a neat roll. He turns out of the roll, flicking his trident and turning it mid lunge as it catches the rouges blade spinning it off into the night. He casts his net. It splays out towards the figure, grasping them and tangling them in its weight. Without their blade, the fight did not last long after that.

The triton swings from the rope attached to the mast, with one deft hand he flings his net at the pirate on the other deck. It lands, and before they can cut it away he releases the rope and spears their restrained form with his trident. Quickly, he pulls a second net from his belt and casts it at his next foe, quickly followed by his thrown trident impaling them to the ships helm behind them. He drags his net off the first corpse and continues his bloody dance across the ship.

A man sits at the docks, carefully, dexterously weaving the costly adamantine fibers into the rope of his net. He sets the heavy weights on the ends and gazes at his handiwork. Even the strongest of foes will struggle to cut their way free or shake off his mastercrafted weapon. His friend turns to him, "You'll for sure lock em down with that one. They had best hope they can dodge.". He replied quietly, almost under his breath but loud enough for his friend to strain to hear him, "They won't get the chance if I'm quick enough.". And so he picks up the heavy net as if it was weightless and begins to walk to the training area at the beach where the floating dummies bobbed and weaved with the waves.  

Masters of the Net and Trident. The Retiarius is one of the least well known schools of fighting, trained to use their speed to evade more heavily armored foes and capture them in their net before slaying them with their tridents. This class of warrior came about from the uprising of a group of fisherman slaves who trained with the tools they had at hand to overthrow a pirate king. The retiarii are a small group of fighters who honor this tradition and often vow to not use conventional weapons, despite being masterful fighters.

Net and Trident

At 3rd level when you take this martial archetype, you gain proficiency with the net and the trident. Being within 5 feet of a creature does not impose disadvantage on your ranged attacks with your net. You also gain the ability to wield these two weapons in a deadly combination. While wielding both your net and trident you gain a +1 bonus to your AC. You may use your net in tandem with your trident, as such when you use the attack action and make an attack using your net you may use your bonus action to attack with your trident.

You also ignore the following restriction on using nets: When you use an Action, Bonus Action, or Reaction to Attack with a net, you can make only one Attack regardless of the number of attacks you can normally make.

Dodge and Disarm
When you take up this archetype, you learn to use your speed and weapons to your advantage, allowing you to dodge quickly and disarm your opponents.

When an enemy creature makes an attack against you while you are not wearing heavy armor you may use your reaction to dodge the attack. Roll an Acrobatics check and divide the outcome by 5, rounding up (minimum +1) and add this to your AC. If you are wearing light armor or are unarmored you may divide your check by 3 instead. Potentially turning a hit into a miss. You make this choice before the DM says whether the attack hits or misses.

If you successfully dodge while you are wielding your net and/or trident you may attempt to disarm the creature (if using your trident), or restrain the creature (if using your net). 
Disarm: Make an attack roll with the trident, on a successful hit, the target makes a strength saving throw (DC = 10 plus your strength modifier plus your proficiency bonus}}). On a failed save the target drops the weapon used to attack you. A creature not holding a weapon cannot be disarmed. A creature holding a weapon with two hands gains advantage on their saving throw to keep a hold of their weapon. This attack deals no damage.
Restrain: Make an attack roll with the net, on a successful hit the creature is restrained by your net.

Reach and Range

You become a master of managing both range and melee combat with your weapons. 

Three-pronged strike: You become more deadly with your trident. The first time on your turn that you successfully hit with an attack roll with your trident add 1d4 piercing damage. This damage increases to 1d6 at level 15. Your trident can benefit from the polearm master feat. 

Weighted Net: You maximise the effectiveness of your net throws to not only restrain but deal damage to your enemies. When you make an attack with your net, on a successful hit the net does 1d4 bludgeoning damage plus your strength modifier. Additionally, the save DC for your net becomes 8 + your proficiency bonus + your strength modifier.

Fetch and Fix

At level 10, you have perfected the art of making and caring for your nets. Whenever a creature escapes your net by damaging it, you may use your reaction to move up to 15 feet towards your net and retrieve it. While you have your damaged net in your possession, you may use your action to do rapid repairs restoring it to functionality, but it's DC and AC are reduced by 2 until you can spend 1 hour fully repairing it. This can stack. If your nets AC reaches 0 it cannot be repaired. Proficiency with weavers tools improves your skill, you can repair your net as a bonus action instead. 

You may also spend 50gp and 4 hours on your net to upgrade its Heft, Hardness and Health. For every 4 hours and 50gp you spend you can increase the DC or AC of your net by 1, or it's HP by 2. Proficiency with weavers tools reduces time and cost spent by half. Your nets DC and AC cannot exceed 19. Your nets HP cannot exceed 25.
When your nets DC is equal 19, you increase the weight of it's stones causing creatures affected by it to have disadvantage on saves against its restraint.
When your nets AC is equal to 19, you have reinforced it with adamantine, it becomes immune to critical hits.
When your nets HP is equal to 25, you have woven magical thread through its construction, it becomes resistant to slashing damage from non-magical weapons that aren't adamantine.

Speed and Skill

Your aim is to catch and kill your foe swiftly. You add your proficiency bonus to your initiative. You have advantage on attack rolls to restrain a creature with your net if the creature hasn't taken a turn in the combat. In addition, if the creature is surprised you may add 1d8 to the attack roll. When you restrain a creature with your net, you can use a bonus action to move up to 15 feet towards that creature.

Catch and Kill

Whenever you make an attack with your trident against a target restrained by your net you gain the following benefits:

You add your proficiency bonus to your damage rolls.
You critically strike on a roll of 19 or 20.
Whenever you critically strike you wound the target, causing them to bleed. At the start of their next turn they take 1d6 piercing damage. This effect can stack.