This was back in the mid 1980s. UNM started out at the 20 on a touch back, then when they got the ball to the 29 and a half yard line, the sticks were brought out to measure and the Lobos got the first down by the nose of the football. I recall Jason Buck running up to the ref and pointing to the 20 and then to the ball that was a half yard short of the 30 and ask how it could be a first down if, by the lines on the field, they were short. In perhaps the first time I've seen a reversed call, the refs took the first down back and called it fourth down.
Kudos to Buck in the situation for his awareness.