#77 had forward momentum after he miraculously recognized an interception despite having his focus fully on the defensive line in front of him, regardless of the fact that he really was not engaged in any blocking.
Like I said, he recognizes the interception, takes 2-3 steps forward at which point the SS already crosses his path. It is very difficult for an offensive linemen to slow his body down enough to make that 180 degree turn and then take the exact proper angle to make the tackle 15 yards down field. What makes this video even more unbelievable is the fact that offensive lineman actually turned on a dime without any slow down in motion.
I'm not making an attempt to discredit your knowledge or anything, but have you played on the offensive line before or coached offensive linemen? Playing on the line, you're usually not in-tune with the whole offense. Your primary focus is on anybody coming into your lanes, opening holes for the runningbacks, and protecting the quarterback long enough for him to get rid of the ball. Very rarely is the offensive linemen that quick to react to an interception. We're usually the last men to recognize the interception let alone make it all the way down the field taking the proper angle to make the touchdown saving tackle. We're not coached on proper angles for tackles as much as we are on blocking technique and what not. It's usually the last thing you work on if you even work on it in the first place.
In this video there is no way that the SS should not have turned it into a pick six. The offense had nobody else on that side of the field. The QB made a horrible mistake throwing amidst the blanket of defenders. It was a wide open lane all the way to the endzone just as long as the receivers on the opposite side of the field do not get free and/or take the proper angle. Most interceptions are not returned for a touchdown because most pro offenses don't make the mistake of flooding one side of the field with receivers leaving one side with only one receiver amidst that many defenders. That was a disaster waiting to happen for the offense and the QB.