HAMSTRING [Rogue]

Your sneak attacks target can wound an opponent's legs, hampering his or her movement.
Prerequisite: BAB +4, Sneak Attack class ability.
Benefit: If you hit with a sneak attack, you may choose to forgo +2d6 of your sneak attack damage to reduce your opponent’s land speed by half.  Other forms of movement (fly, burrow, and so forth) aren’t affected.  The speed reduction ends when the target receives a successful Heal check (DC 15), any cure spell, or other magical healing, or after 24 hours, whichever comes first.  A hamstring attack does not slow creatures that are immune to sneak attack damage or those that have either no legs at all or more than four legs.  It takes two successful hamstring attacks to affect a quadruped.