Oracle Text

Cast this spell only during combat before blockers are declared.

Untap target attacking creature and remove it from combat. Gain control of that creature until end of turn.

Card Rulings

10/4/2004 Disharmony works even if the attacker was not tapped to attack.
10/4/2004 The creature untaps (if it was tapped) before you get control of it.
10/1/2008 The current wording explicitly removes the creature from combat. It is no longer an attacking or blocking creature.
10/1/2008 Disharmony can target a creature you control.
10/1/2009 If you cast Disharmony during an opponent’s turn, you may then block with the creature you gain control of (assuming there’s an attacking creature it can block).
9/20/2013 If a turn has multiple combat phases, this spell can be cast during any of them as long as it’s before the beginning of that phase’s Declare Blockers Step.