2015-06-22 : Throwing Knife is the source of the damage dealt because of its triggered ability. For example, you could sacrifice Throwing Knife to deal 2 damage to a creature with protection from red, even if Throwing Knife is equipped to a red creature.

2015-06-22 : Throwing Knife’s triggered ability triggers before blockers are declared. If you use the ability and destroy the targeted creature with lethal damage, it won’t be on the battlefield to block.