506.1.
The combat phase has five steps, which proceed in order: beginning of combat, declare attackers,
declare blockers, combat damage, and end of combat. The declare blockers and combat damage
steps are skipped if no creatures are declared as attackers or put onto the battlefield attacking (see
rule 508.4). There are two combat damage steps if any attacking or blocking creature has first strike
(see rule 702.7) or double strike (see rule 702.4).
506.2.
During the combat phase, the active player is the attacking player; creatures that player controls
may attack. During the combat phase of a two-player game, the nonactive player is the defending
player; that player and planeswalkers he or she controls may be attacked.
506.2a
During the combat phase of a multiplayer game, there may be one or more defending
players, depending on the variant being played and the options chosen for it. Unless all the
attacking player‘s opponents automatically become defending players during the combat phase,
the attacking player chooses one of his or her opponents as a turn-based action during the
beginning of combat step. (Note that the choice may be dictated by the variant being played or
the options chosen for it.) That player becomes the defending player. See rule 802, «Attack
Multiple Players Option,» rule 803, «Attack Left and Attack Right Options,» and rule 809,
«Emperor Variant.»
506.2b
In the Two-Headed Giant multiplayer variant, the nonactive team is the defending team. See
rule 810, «Two-Headed Giant Variant.»
506.3.
Only a creature can attack or block. Only a player or a planeswalker can be attacked.
506.3a
If an effect would put a noncreature permanent onto the battlefield attacking or blocking, the
permanent does enter the battlefield but it‘s never considered to be an attacking or blocking
permanent.
506.3b
If an effect would put a creature onto the battlefield attacking under the control of any player
except an attacking player, that creature does enter the battlefield, but it‘s never considered to be
an attacking creature.
506.3c
If an effect would put a creature onto the battlefield attacking either a player not in the game
or a planeswalker no longer on the battlefield or no longer a planeswalker, that creature does
enter the battlefield, but it‘s never considered to be an attacking creature.
506.3d
If an effect would put a creature onto the battlefield blocking but the creature it would block
isn‘t attacking either the first creature‘s controller or a planeswalker that player controls, that
creature does enter the battlefield, but it‘s never considered to be a blocking creature.
506.4.
A permanent is removed from combat if it leaves the battlefield, if its controller changes, if it
phases out, if an effect specifically removes it from combat, if it‘s a planeswalker that‘s being
attacked and stops being a planeswalker, or if it‘s an attacking or blocking creature that regenerates
(see rule 701.12) or stops being a creature. A creature that‘s removed from combat stops being an
attacking, blocking, blocked, and/or unblocked creature. A planeswalker that‘s removed from
combat stops being attacked.
506.4a
Once a creature has been declared as an attacking or blocking creature, spells or abilities that
would have kept that creature from attacking or blocking don‘t remove the creature from
combat.
506.4b
Tapping or untapping a creature that‘s already been declared as an attacker or blocker
doesn‘t remove it from combat and doesn‘t prevent its combat damage.
506.4c
If a creature is attacking a planeswalker, removing that planeswalker from combat doesn‘t
remove that creature from combat. It continues to be an attacking creature, although it is
attacking neither a player nor a planeswalker. It may be blocked. If it is unblocked, it will deal
no combat damage.
506.4d
A permanent that‘s both a blocking creature and a planeswalker that‘s being attacked is
removed from combat only if it stops being both a creature and a planeswalker. If it stops being
one of those card types but continues to be the other, it continues to be either a blocking creature
or a planeswalker that‘s being attacked, whichever is appropriate.
506.5.
A creature attacks alone if it‘s the only creature declared as an attacker during the declare
attackers step. A creature is attacking alone if it‘s attacking but no other creatures are. A creature
blocks alone if it‘s the only creature declared as a blocker during the declare blockers step. A
creature is blocking alone if it‘s blocking but no other creatures are.
506.6.
Some spells state that they may be cast «only [before/after] [a particular point in the combat
phase],» in which that point may be «attackers are declared,» «blockers are declared,» «the combat
damage step,» «the end of combat step,» «the combat phase,» or «combat.»
506.6a
A spell that states it may be cast «only before (or after) attackers are declared» is referring to
the turn-based action of declaring attackers. It may be cast only before (or after) the declare
attackers step begins, regardless of whether any attackers are actually declared. (See rule 508.)
506.6b
A spell that states it may be cast «only before (or after) blockers are declared» is referring to
the turn-based action of declaring blockers. It may be cast only before (or after) the declare
blockers step begins, regardless of whether any blockers are actually declared. (See rule 509.)
506.6c
Some spells state that they may be cast only «during combat» or «during a certain player‘s
combat phase» in addition to the criteria described in rule 506.6. If a turn has multiple combat
phases, such spells may be cast at an appropriate time during any of them.
506.6d
Some spells state that they may be cast «only before (or after) [a particular point in the
combat phase],» but don‘t meet the additional criteria described in rule 506.6c. If a turn has
multiple combat phases, such spells may be cast that turn only before (or after) the stated point
of the first combat phase.
506.6e
If a spell states that it may be cast «only before [a particular point in the combat phase],» but
the stated point doesn‘t exist within the relevant combat phase because the declare blockers step
and the combat damage step are skipped (see rule 508.6), then the spell may be cast only before
the declare attackers step ends. If the stated point doesn‘t exist because the relevant combat
phase has been skipped, then the spell may be cast only before the precombat main phase ends.
506.6f
If a spell states that it may be cast «only during combat after blockers are declared,» but the
declare blockers step is skipped that combat phase (see rule 508.6), then the spell may not be
cast during that combat phase.
506.6g
Rules 506.6 and 506.6a–f apply to abilities that state that they may be activated only at
certain times with respect to combat just as they apply to spells that state that they may be cast
only at certain times with respect to combat.