What Texas had against A&M in roughly ‘05 was an offensive conversion safety. A&M blocked an extra point, recovered the live ball in the field of play, carried it back into the end zone, and was tackled. One point to the Horns. That has happened three times (I think) in I-A, including once in the Fiesta Bowl recently, and many more times in other levels of college FB.
In theory, the same can happen in the other end zone. OSU gets the ball during a Horns EP (blocked kick, recovered fumble, or INT) and runs the live ball all the way back to the 5, then fumbles. Horns recover the live ball in the field of play, run backwards into the end zone, and get tackled. Or, a Horn intentionally bats the live ball out of the end zone. Either way, that’s a safety for the Cowboys. But because it happened on a conversion, they only get one point.