GURPSよろず

Aggressive Parry
Hard
Default: prerequisite skill Parry-1.
Prerequisite: Boxing, Brawling, or Karate; cannot exceed prerequisite Parry.

Only a few “hard” styles teach this tactic. Instead of merely deflecting a blow, you attempt to injure your attacker with an especially forceful parry. This is incompatible with Cross Parry (p. 121).
Roll against Aggressive Parry to defend, at the usual -2 for Boxing vs. a kick, or -3 for Boxing or Brawling vs. a swung weapon. You cannot retreat. Failure means you’re hit; your attacker may choose to hit his original target, your parrying arm, or your parrying hand. Success means you parry and may roll against the underlying skill to strike the attacking body part or weapon, modified as follows.

Modifiers: Against unarmed, -2 to hit an arm or leg, -4 to hit a hand or foot; -2 for Boxing vs. a leg or foot; -1 if your foe knows Rapid Retraction (p. 51). Against armed, a basic -3; another -3 to -5 for weapon size (see p. B400); a further -3 for Boxing or Brawling vs. a swung weapon.

Success on this skill roll inflicts thrust-4 crushing damage or thrust-2 at -1 per die, whichever is worse, on the targeted weapon or body part. Skill bonuses apply normally. Failure means you didn’t parry forcefully enough to inflict damage.
Weapon parries against unarmed attacks are essentially aggressive “for free”; see Parrying Unarmed Attacks (p. B376).