I walk to the line of scrimmage saying to myself, "The snap is on two, it's on two." As I get into my crouch and put down my hand, I try to gauge the defense, which determines my blocking assignment, all the while saying to myself, "On two, on two."

I can hear the quarterback's cadence and what the right tackle is saying five people away. Out of the corner of my eye, I can see a linebacker step onto the line of scrimmage, keying me that a blitz is coming.

I've totally lost that there are 75,000 people screaming in the stands, though the sound can be deafening. When I can't hear, I have to be very aware of the football, which I can barely see out of the corner of my eye. Sometimes I get fooled by the flash of a helmet, which can draw me offsides.

I never look at a player's eyes. It's too personal, especially since I'm about to smash the guy as hard as I can.

I can see his elbow down to his hand. I can see his knees down to his feet. I read the angle and width of his stance to see if he's going to play head up, pinch inside, or burst off the ball. Sometimes you're helmet to helmet with a player and you can literally smell his breath.

Ten 300-pound guys are engaged in hand-to-hand combat in the box which is seven yards wide and three yards deep. But everything is very well orchestrated and you don't really notice anyone else until the play ends and everybody is in a pileup on the ball. Then you can tell what's happening by listening. If we're at home and the crowd's roaring, I know we've just had a good run or completed a pass. Away, a roar means they've stuffed us for a big loss.

I smack into the defensive lineman with my face mask. It's hard to get used to aiming your face to hit it right into somebody. Your neck snaps and, hopefully, so does his. Your hands are on his chest and you can tell in the first second—if his helmet pops back or if he pops yours back—whether or not you're going to win that block.

Andy Heck is an offensive tackle for the Chicago Bears.