Trolls were abroad, no longer dull-witted, but cunning and armed with dreadful weapons.

Olog-hai Crusher

Trample
This creature can't block unless you control a Goblin or Orc.

The Lord of the Rings: Tales of Middle-earth

Trample
Olog-hai Crusher can't block unless you control a Goblin or Orc.

The Goblin or Orc you control doesn't have to block.

Whether you control a Goblin or Orc matters only at the time you declare blockers. Once Olog-Hai Crusher blocks a creature, that won't change even if all the Goblins and Orcs you control leave the battlefield.