Fai always made sure to track someones movements especially in a fight or in this case a snowball fight. He was a good fighter for a reason. So when the snowball came flying he knew to duck and move to a better position, this time with a place to use as a defence should he need it.

It gives him time to gather snow a create a good few snowballs before to keeps an eye some more, using a good enough moment to fling two snowballs at the same time.