GURPSよろず

Riposte
A gambit popular with martial artists is a parry that carries the attacker’s weapon out of line or otherwise compromises his defenses, “setting up” a counterattack – or riposte – that exploits the opening. Executed correctly, the riposte is difficult to avoid. However, it often requires the defender to begin his attacking motion early and give up some of his own ability to defend. Thus, it can backfire spectacularly!
To set up a Riposte, declare that you wish to do so before you parry. Choose a penalty to your Parry score – the larger the penalty, the greater your focus on the counterattack. This cannot reduce your Parry, before all other modifiers except Enhanced Parry, below 8.
Then add the remaining modifiers and try to parry the attack. You can retreat – but if your foe steps back after attacking, you might end up too far away for a Riposte.
Success means you parry and set up a Riposte. If your first attack next turn uses your parrying weapon against the foe you parried, one of his active defenses against it suffers the penalty you accepted on your parry. If you parried his hand or weapon, reduce his Parry with that hand (with either hand, if his attack used two hands). If you parried his shield, lower his Block. If you parried an unarmed attack other than a hand strike (bite, kick, slam, etc.), reduce his Dodge. Apply half this penalty (drop fractions) to any other defense he attempts against your attack – including rolls to resist grappling moves that use Quick Contests instead of active defenses (e.g., takedowns).
Failure means you’re hit, as for any failed parry. Your attempt gives you no special benefits – although you can still attack your foe on your next turn, if his attack leaves you in any shape to do so.

Example: Harry the Good and Black Odo are dueling with broadswords and medium shields. Harry has Broadsword-16 and Enhanced Parry 1, for a Parry of 12. Odo attacks Harry with his sword and Harry decides to attempt a Riposte. Odo being his mortal enemy, Harry goes for broke and takes the maximum penalty: -4, which drops his Parry to 8. With +1 for Combat Reflexes and +2 for his shield’s DB, his final Parry is 11. He succeeds, warding off Odo’s attack. This allows him to Riposte with his sword (not a shield bash, kick, etc.) on his turn. He does so and succeeds! If Odo tries to parry with his sword, he has the same penalty Harry did, or -4. If he attempts a dodge or block, he has half this penalty, or -2.

A Riposte is most effective when you’re more skilled than your foe, when you have many defensive bonuses (Combat Reflexes, shield, weapon with a Parry bonus, etc.), or when your target is already compromised – e.g., kneeling or on bad footing.
The active defense penalties from Riposte and from feinting are cumulative. If on your turn you successfully feint a foe, and on his turn he attacks and you parry at a penalty, then you can Riposte on your next turn, forcing him to defend with penalties for both the feint and the Riposte. This takes two turns and offers many opportunities for failure . . . but when it works, it’s devastating!
You cannot combine Deceptive Attack and Riposte, though. A Riposte is a Deceptive Attack – just one where you’re taking a defensive risk instead of an offensive one.