Why did buck avoid getting into a fight with Spitz even though he hated him

Buck wasn't ready to fight.... Spitz fought other dogs without honor, he cheated. Buck could never forget this fact and had to be prepared to fight the same way.

So that was the way. No fair play. Once down, that was the end of you. Well, he would see to it that he never went down. Spitz ran out his tongue and laughed again, and from that moment Buck hated him with a bitter and deathless hatred.