Ranger passive feat ability - Knee-Capping
Knee-Capping is a ranger ability acquired through the sharpshooter feat tree. If feat points are invested into this feat, the ranger is granted a passive chance when he/she attacks or uses a combo to root his target for 3 seconds, preventing further movement.
Knee-Capping is the last part of a chain of crowd-control(cc) feat abilities. In order to be able to invest feat points to it, you first have to complete the ricochet and tendon rupture feats. It is very useful against close-combat enemies, given that the chance to proc is fairly good, although its usefulness against ranged or spellcasters is limited and can only offer an escape opportunity or a way to catch up with a running foe and still have time to use a combo.
As of patch applied on June 2nd 2008, when this ability procs, it no longer gives root immunity to the target after it expires, leaving the target exposed to further rooting by another proc, or by other abilities.