loser's rate. What it doesn't fully account for are things like turnovers. A turnover is simply a non-successful play for the offense.
So if you have an offense that is gaining 8+ yards per play, they will have a high success rate even if they turn the ball over 10 times. It also can give bonus points for very successful plays, so a 3 play, 82 yard TD drive isn't going to do much to bring up your success rate. At least not nearly as well as a 16 play, 82 yard drive would.
Put another way, a 3 play 82 yard TD drive followed by a 3-and-out can easily have a combined lower success rate than two 7-play punt drives.
It's an imperfect stat that may or may not tell a story.
BYU's scoring drives were:
3 plays, 82 yards (100% success)
5 plays, 73 yards (60% success)
4 plays, 75 yards (50% success)
5 plays, 15 yards (80% success)
Only other notable drive for BYU was a 35 yard, 13 play missed FG. 5 out of 12 plays successful.