In combat, you make a Called Shot at a specific part of the opponent's body. This increases the Difficulty by 2, but it can have powerful effects. STs may decide called shots have different effects based on weapon and enemy, but here are the most common ones.
Head +3 automatic damage dice and your attack ignores 2 DT
Eyes (+3 DC) Bypasses armor entirely and blinds target.
Arm The arm is disabled and can no longer be used to wield weapons. This gives +2 difficulty to all attacks with 2-handed weapons, and +2 difficulty to using a 1-hander if it's now in the off hand.
Leg The leg is disabled, slowing the movement speed to a crawl and giving +2 difficulty to dodging. For Unarmed attacks, a called shot at the leg will knock the fighter down, requiring a Minor Action to stand back up.
Groin The pain of the attack makes the target lose an additional -2 dice on top of their normal Wound Penalties