SB Nation's BYU blog Vanquish The Foe discusses the details that led Air Force to beating BYU on Saturday:
As I said coming into this game, Air Force was not tested in their first week, and I knew there would be some new gadget plays this week that would test BYU's discipline. Test failed. While it didn't take trick plays to beat us, Air Force scored on three gadget plays against the Cougars today, and there is no excuse for any of them working. But let's talk about what set it all up.
When you face Air Force's option, job #1 is stopping the fullback on the dive play. It is critical to take away the dive as an option and string plays out to the sideline. We did not stop the dive at all today. Jared Tew, the Falcon fullback, averaged 4.5 yards a carry today. Our defensive line was getting pushed back fairly consistently and our middle linebackers were overrunning the dive angle. This is a bad combo that led big chunks up the middle.
The fullback dive is the key to any option offense since it can become a boring game for the defense, and after multiple dives the secondary and linebackers bite on a fake and then it is too late for them to recover because it could be a pass play or an option to the outside.
BYU's defense did lose some good players on that side of the ball from last year and highly touted freshman linebacker Zac Stout saw his first significant time against Air Force and seemed lost. The key to managing an offense like Air Force is to play disciplined football.