Giants in the TT are a bit special. They don't attack like every other unit in the game. You instead roll on lists with weird special attacks. One for small targets one for large targets.
One of these attacks is
Yell and Bawl
The Giant yells and bawls at the enemy.
This is not a pleasant experience, as Giants
are deafeningly loud and tend towards poor
oral hygiene. Neither the Giant nor models in
contact with him actually fight if they have
not already done so this round.
The Giant's side automatically wins the combat.
Basically the giant automatically wins the engagement and his enemies have to take a leadership test to see if they break or not.
All of the giants attacks we've seen so far are based on his TT rules which is an awesome detail imho.
The others are
Swing with Club, Squash and
Eat.