Touka said:
To me it looked like Guts stopped his swing so he wouldn't hit Casca, and Griffith knew he would do this. I'm not sure if the blade actually touched Griffith, otherwise his hair—which is between his body and Guts' sword—would have been sliced. We saw in 366 that Guts manages to cut a strand of Griffith's hair, so it isn't invincible. I think Guts stopped his swing so he wouldn't cut Casca in half, otherwise he might have been able to hurt Griffith.
Remember, he is still in control (the armor didn't even activate), so if he did stop on his own, it was because he knew he *couldn't* hurt Griffith; he tried enough times by now to realize it.