Defender is one of the two available Sword & Shield Mastery alongside Swordmaster in New World. Defender skill tree mainly focus on boosting the player's defensive capabilities by increasing armor and reducing incoming damage from various sources. It is more shield-oriented than Swordmaster. Sword & Shield mainly benefit from Strength, but Dexterity also contributes although on a secondary level.
All Defender Abilities in New World
Defender Tree Active Abilities

Shield Rush
Rush forward 5 meters, knocking back foes and dealing 125% weapon damage.
Cooldown: 20 seconds
Upgrades:
Improved Rush: On successful hit, all enemies within 5m are weakened by 10% for 10s. (Weaken reduces damage)
Intimidating Rush: On successful hit, all enemies within 5m of you are 30% Slowed for 4s. (Slow reduces movement speed)

Shield Bash
Deals 50% weapon damage and stuns foes in front of you for 2s
Taunt Gem Compatible: If you have a Carnelian gem equipped in your sword, this ability cause a 6s taunt to all enemies hit.
(Taunt causes monsters to focus only on you)
Cooldown: 25 seconds
Upgrades:
Intimidating Bash: Shield bash causes greatly increase threat and 100% more damage.
Concussive Bash: Shield Bash stun duration increased by 1s

Defiant Stance
For 8s, reduce the incoming base damage for attackers by 30%.
Taunt Gem Compatible: If you have a Carnelian gem equipped in your sword, this ability cause a 6s taunt to all enemies within 8 m.
(Taunt causes monsters to focus only on you)
Cooldown: 45 seconds
Upgrades:
Final Count Down: If your health is above 50% damage reduction, increased by 20%
Restoration: Gain 15% of your max health when Defiant Stance ends.
Defender Tree Passive Abilities

Sturdy Shield
Shields provide 15% more armor.

Elemental Resistance
Reduce damage from all magical types by 10%.

One With The Shield
When you block with a shield, all shield skills recharge 1%

Final Blow
The 3rd attack in your light attack combo deals 15% more damage and generates more threat.

Sturdy Grip
Stamina damage is reduced by 15% when blocking a melee attack with a shield.

Defensive Training
When you block an attack gain 10% Fortify for 5 seconds.

Fortitude
While holding a Sword current and max health are increased by 10%.

Recuperation
All incoming healing and regeneration increased by 10%.

High Grip
Stamina damage is reduced by 15% when blocking a ranged attack with a shield.

Defensive Formation
While blocking reduce damage to all other allies within 2 meters by 30%.
(1 second cooldown)