If it looks like there's "a second back judge" in the NFL preseason games this week, you're not mistaken. The league is, for a second straight year, experimenting with adding an eighth official to its games, and they're using the second week of the preseason to do it.
What the league is calling a "middle judge" will be positioned 18 to 20 yards downfield in every game this week. Their primary responsibilities will be to watch the middle of the line -- the center and the two guards. They'll also watch for defensive and offensive holding downfield, which will be particularly useful on longer run plays.
So more than "a second back judge," the middle judge is like a "deep umpire." The umpire has been moved to the offensive side of the ball, opposite the referee.
It also won't hurt to have another set of eyes downfield on passes. This will make Richard Sherman happy. The Seattle Seahawks cornerback has called for an eighth official to be 20 yards downfield to help with those pass plays. If the middle judge reads pass, his focus will then train on his area of the field and then to the intended receiver of a pass.
"We are going to look at positioning the eighth official opposite the back judge," NFL Senior Vice President of Officiating Dean Blandino explained on the league's website. "We want to try to fill some of the holes that may happen in specific situations over the course of a game."
The NCAA has recently added an eighth official, called a center judge, to some of their games. It's widely adopted across Division I, so you've seen them on Saturdays for a couple years. In the NCAA's version, the umpire stays behind the defensive line and the center judge is about 12 yards behind the offensive line, outside the shoulder of the tackle. The center judge's primary responsibilities are spotting the ball, watching the line play and any action ahead of the runner to their side.
Last year the NFL experimented with both the NCAA's version and the addition of the middle judge; this preseason they're giving the middle judge a second look.