Rulings

• 2010-06-15
  You're the defending player if a creature is attacking you or a planeswalker you control.
• 2010-06-15
  For each unblocked creature attacking you, you must put a Plant token onto the battlefield blocking it, even if you don't want to.
• 2010-06-15
  The Plant token blocks the attacking creature even if the block couldn't legally be declared (for example, if the attacking creature has flying).
• 2010-06-15
  Putting a blocking creature onto the battlefield doesn't trigger "Whenever a creature blocks" abilities. It also won't check blocking restrictions, costs, or requirements.
• 2010-06-15
  Putting a blocking creature onto the battlefield will trigger "When this creature becomes blocked by a creature" abilities. It will also trigger "When this creature becomes blocked" abilities in this case, because the attacking creature had not yet been blocked that combat.
• 2010-06-15
  The last ability triggers only if four or more creatures were declared as attackers during your opponents' declare attackers step. Only creatures attacking you are counted; creatures attacking your planeswalkers are not. The creatures may be controlled by different players.