If revenge had ruled Sandor’s heart, he would have continued fighting. Gregor, after all, showed no sign of obeying the king. Sandor, after he killed his brother, could protest he was merely protecting the unarmed Ser Loras from Ser Gregor’s unprovoked attack. He would have obtained the value that he held higher than any other: an eye for an eye. His lifelong suffering was worse than any death, and in killing his evil brother, he would have been re-establishing the correct order of things, not only in his own life, but in the social and political spheres of Westeros as well.
But the Hound did not continue to fight. He dropped his knee, bowed his head, and even at this time of personal peril, demonstrated his fealty to King Robert. He had no way of knowing his brother’s sword would miss his head by mere centimetres. Thus, his demonstration of loyalty to king and kingdoms could have been the final heroic act of his life. He must have known this, but he took this life-and-death risk anyway, regardless of the consequences.
The significance of the tournament sequence, I believe, is that Sandor lives his life according to principles he will not compromise. These virtues are more meaningful to him - and therefore to Game of Thrones - than the childish precepts of retributive justice.
Pearson Moore ~ The Seventh Sword: The Chivalry of Sandor Clegane
from his book Game of Thrones Season Two Essays
That’s my boy Sandor, right there.
Points to take away from this: Sandor has certain principles; some things are more important to him than revenge, despite his claims; the books themselves consider these things more important and meaningful than revenge.