Tyr knew he had to get Kolbeinn down or Kolbeinn would die as he was already unconscious.
He was not at full strength and could barely use his sledgehammer yet a monster that could defeat Kolbeinn was rampaging.
Tyr realized at that moment that they had found the ax he had planted, and Gissur had responded in a way he could not have foreseen.
They had launched the first attack and this attack was in no way just a warning, he intended to crush them with this and judging by the number of men he allocated.
Gissur was in no way underestimating them.
Gudrun became a target eventually, the Mad Hound grabbed an enemy and crushed him between his hands before throwing him like a pebble in Gudrun's direction.
The speed and force with which he did allow Kolbeinn to slip between his hands, crashing into the snow beneath.
"Clumsy me! Here!" The giant joked as he tried to stomp Kolbeinn to death but his foot met no mass.