Back Story

OK, trying the National Novel Writing Month (NaNoWriMo) - so I might have a few more thoughts than normal. (Insert empty head joke here) I am rapidly growing a healthy, nay admirable, respect for the author that can reveal a complex back story without resorting to a load of exposition. How do you reveal the details without killing the pace of the story?

"He hit him."

"The grey-green sun shined off the sweat specked scales of his opponent as the boot-camp entrenched typical gut punch landed."

I've got to find a happy medium in there.