Throwing Knife — ruling 1

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.

Throwing Knife — ruling 2

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.

Throwing Knife : règles, fonctionnement et interactions (MTG)

Throwing Knife is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Equipped creature gets +2/+0. Whenever equipped creature attacks, you may sacrifice this Equipment. If you do, this Equipment deals 2 damage to any target. Equip (: Attach to target creature you control. Equip only as a sorcery.)

How it works : Throwing Knife

Original English text — Wizards of the Coast / Scryfall

#1June 22, 2015· Wizards of the Coast
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.
No other card is named in this ruling.
#2June 22, 2015· Wizards of the Coast
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.
No other card is named in this ruling.