509.1. First, the defending player declares blockers. This turn-based action doesn't use the stack. To declare blockers, the defending player follows the steps below, in order. If at any point during the declaration of blockers, the defending player is unable to comply with any of the steps listed below, the declaration is illegal; the game returns to the moment before the declaration (see rule 723, "Handling Illegal Actions").
509.1a. The defending player chooses which creatures they control, if any, will block. The chosen creatures must be untapped. For each of the chosen creatures, the defending player chooses one creature for it to block that's attacking that player or a planeswalker they control.
Provoke technically affects 509.1c but Provoke doesn't overwrite 509.1a
And this covers the Team variants:
805.10d. As the declare blockers step begins, the defending team declares blockers. Creatures controlled by the defending players can block creatures attacking any player on the defending team or attacking a planeswalker controlled by one of those players. The defending team has one combined block, and that set of blocking creatures must be legal as a whole. See rule 509.1.
509.1a. The defending player chooses which creatures they control, if any, will block. The chosen creatures must be untapped. For each of the chosen creatures, the defending player chooses one creature for it to block that's attacking that player or a planeswalker they control.
Why doesn't it overwrite 509.1a?
How is this card meant to be used then? To force an opponent to block with one of their creatures?
Provoke's effect requiring the targeted creature to "bloc[k] this turn if able" is governed by C.R. 509.1c. Normally, the defending player chooses which creatures will block (C.R. 509.1a). However, if that creature is affected by Provoke and is otherwise able to block, it must block even if the defending player doesn't want it to (C.R. 509.1c). Provoke changes only whether that creature must block, not what it must block, which the defending player is still free to choose (but only to the extent that player could do so if Provoke weren't in effect) (compare Provoke with Hunt Down).
How is this card meant to be used then? To force an opponent to block with one of their creatures?
Although this is not a rules questions, answering it may still help you understand the game more. Provoke's most common (unique?) usage is to get rid of a nasty creature by forcing it to make an undesirable block. Plasma Elemental, for example, would keep attacking you, and never dare to block, of course... unless provoked.
can I use Provoke on an opponents creature to block another opponents creature attacking me?
As far as I can tell, there exists only one way (yet?) to have an opponent's creature block on your behalf: you must first steal that creature, and then block with it (as it has become YOUR creature now).
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules
509.1a. The defending player chooses which creatures they control, if any, will block. The chosen creatures must be untapped. For each of the chosen creatures, the defending player chooses one creature for it to block that's attacking that player or a planeswalker they control.
Provoke technically affects 509.1c but Provoke doesn't overwrite 509.1a
And this covers the Team variants:
Why doesn't it overwrite 509.1a?
How is this card meant to be used then? To force an opponent to block with one of their creatures?
Provoke's most common (unique?) usage is to get rid of a nasty creature by forcing it to make an undesirable block.
Plasma Elemental, for example, would keep attacking you, and never dare to block, of course... unless provoked.
As far as I can tell, there exists only one way (yet?) to have an opponent's creature block on your behalf: you must first steal that creature, and then block with it (as it has become YOUR creature now).
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules