Blocking

Blocking Creature
A creature becomes a blocking creature when (a) it’s declared as part of a legal block during the combat phase and (b) all costs to block, if any, have been paid. It remains a blocking creature until it’s removed from combat, it stops being a creature, its controller changes, or the combat phase ends. A creature may also be put into play blocking. Blocking creatures don’t exist outside of the combat phase. See rule 309, “Declare Blockers Step.”