Discworld command help
riposte - Stave off an opponent's attack.
riposte <person> with <weapon>
With this command, you attempt to riposte an opponent's attack. As you parry an attack you turn the parry into a thrust.
This means that you prepare yourself for a special riposte attack, then, when you successfully parry an attack you will gain an (almost) free additional attack.
Your ability in fighting.special.weapon determines your ability to prepare, which costs 25 fighting points, while your skill with your chosen weapon determines the efficacy of your riposte. In order to riposte your combat response must be parry.
> riposte warrior with sword
You prepare to riposte against the hairy warrior with the long sword.