Thanks, AB. That makes sense. Is it normal for him to step on the field during measurements?
Out in the middle of the field? No.
But take a look at this measurement, it's on the sideline, or very close to it. He's going to be with the box, so if it's close to the sideline, he'll be in the shot.
And you'll notice, the alternate official, no matter what his normal position, will always wear a black hat.