The first person to say “leave him alone” makes it easier for the next five. Be the first voice.

Silence in a group reads as agreement, even when almost nobody agrees. Everyone is waiting for a sign that objecting is allowed, and one short sentence provides it, which is why the second, third and fourth voices arrive so quickly afterwards. The first one carries nearly all the cost and does nearly all the work.

If you can, keep it to one sentence and skip the speech. Then tell an adult who has some power over the situation. Being the first voice does not mean being the only person responsible.