Weapon Block is a skill designed to help the claw assassin survive. Since she cannot block with two claws equipped, weapon block tries to amend that deficiency for her.
Unlike regular shield block that all characters use while they have a shield equipped, weapon block is not affected either by level or dexterity. Subsequently, it is also not affected by item mods that increase chance of blocking,(though block speed can be increased through faster block rate gear). The only way for the Assassin to increase her block chance when using this skill is to pour more points into it. As with most passive skills, Weapon Block suffers from diminishing returns, and no Assassin will ever reach the block cap for shields (75% chance to block) with this skill. However, unlike normal shield blocking, Weapon Block can block almost any elemental attacks from both PvM and PvP, making this skill nearly indispensable for many assassin PvP builds. (The only skills that weapon block will not block are those that arise from or travel along the ground: blaze, firewall, fissure, and moulten boulder.)
Weapon Block will not work when running or walking. It will only work when standing still, (teleporting), or attacking.