In the second quarter, Texas led TCU by just three points at 10-7. The game was very much still in the balance — the Longhorns had actually just stopped a potential Horned Frog touchdown drive when linebacker Steve Edmond picked off Casey Pachall.
Just six plays later, Texas was up 17-7, thanks to two third-down passes, the first of which set up the second. Here's the first play.
On this third-and-8, keep an eye on the route Marcus Johnson runs out of the middle of Texas's trips formation. The slot receiver (Jaxon Shipley) and the outside receiver (Kendall Sanders) both cleared out, leaving Johnson one-on-one with safety Derrick Kindred. Johnson looks like he's going to run a wheel, then pivots at about six yards and runs an in route. That's a tough route to cover in man coverage, and, with Kindred playing pretty much right at the boundary, he can't get there in time. Johnson catches the ball on the move and makes 12 yards and a Texas first down.
Why was that play important? In addition to earning a first down, it sets up this next play perfectly.
Just three plays later, Texas is facing a third-and-10, and again the Longhorns line up in trips, this time to the left. This play has a slightly different design, but the point is that, for the first few seconds, it looks EXACTLY like the previous play. Operating out of the slot, Jaxon Shipley appears to be running another clear-out route, while Mike Davis is doing the same on the outside. Marcus Johnson is running the beginning of a wheel route.
And that's where everything shifts. First, let's look at what TCU is trying to do. TCU coach Gary Patterson is known to half his coverages, basically deciding to cover each side of the field differently. So it's possible for him to play a Cover 3 (or half of one) to one side, then play a Cover 2 to the other. The player to watch here is cornerback Kevin White. White is supposed to play a deep safety role — when Davis cuts to the inside, he's supposed to hand Davis off if he spots any vertical routes up the sideline. The way the defense is supposed to work is that safety Sam Carter, who is lined up over Johnson, will take Davis when he cuts inside, leaving White to switch to Johnson's vertical route.
From the Texas side of things, Shipley and Davis cut inside — the opposite of the deep routes from above — while Johnson actually runs a wheel, rather than the wheel-pivot route that he ran earlier. White gets sucked inside with Davis (the big mistake on the play), and Elisha Olabode, who is playing a deep safety over the middle of the trips formation, also steps forward on Davis and can't get over in time to mask White's mistake. The result is a wide-open Johnson for a touchdown that helped to break the game open.