Soon after the armies clashed, the wildlings and the mountain clansmen were slowly pushed back. They had far worse equipment, and their shield wall was a bit uneven. The only reason they weren't overwhelmed at the very beginning was the presence of a giant in both flanks and the centre. The giants used tree trunks as clubs to push back the enemy line, sometimes outright smashing some men into meat paste. However, soon after the armies clashed, the giant in the left flank got pierced by a spear in the eye. He died instantly, and the flank started slowly losing ground.