2

I block a Territorial Allosaurus with a Brindle Boar. I sacrifice the Brindle Boar. Does the Territorial Allosaurus still do damage to me?

3

Yes, that works; you won't take any damage, unless the Allosaurus somehow has trample. The Allosaurus remains a 'blocked' creature after the Boar is assigned to block it:

509.1h An attacking creature with one or more creatures declared as blockers for it becomes a blocked creature; one with no creatures declared as blockers for it becomes an unblocked creature. This remains unchanged until the creature is removed from combat, an effect says that it becomes blocked or unblocked, or the combat phase ends, whichever comes first. A creature remains blocked even if all the creatures blocking it are removed from combat.

510.1c A blocked creature assigns its combat damage to the creatures blocking it. If no creatures are currently blocking it (if, for example, they were destroyed or removed from combat), it assigns no combat damage.

After declaring blockers, before the combat damage step begins, there is an opportunity for both players to play instants or activate abilities like the Boar's.

  • 1
    The removed blocker won't deal damage either. – ikegami Mar 17 at 19:41
1

In the situation you describe, no combat damage is dealt because the Allosaurus is blocked. Two things of note:

  1. If you sacrifice your blocker, it won't deal combat damage (unless it has first strike or double strike)

  2. If the attacker has trample, it will still deal damage to you.

The relevant rules are the following:

510.2. all combat damage that's been assigned is dealt simultaneously. This turn-based action doesn't use the stack. No player has the chance to cast spells or activate abilities between the time combat damage is assigned and the time it's dealt.

509.1h An attacking creature with one or more creatures declared as blockers for it becomes a blocked creature; one with no creatures declared as blockers for it becomes an unblocked creature.

510.1c A blocked creature assigns its combat damage to the creatures blocking it. If no creatures are currently blocking it (if, for example, they were destroyed or removed from combat), it assigns no combat damage.

702.19c If an attacking creature with trample is blocked, but there are no creatures blocking it when damage is assigned, all its damage is assigned to the player or planeswalker it's attacking.

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