One of the keys for success in the West Coast passing schemes is the underneath routes designed to create match up issues for the opposing defense. This is the primary reason why Scot Loeffler prefers to have his wide-receivers crossed-trained to play all the WR positions. This will allow him to move his personnel around to create possible miss matches with the opposing secondary. Imagine if you will, a safety or LB matched up with one of Auburn's more athletic or speed receivers.
On this particular play, Temple faces a 1st & 10, which is primarily a "rushing" down. The Owls will execute a play-action pass from a 3-WR set and TE. At the snap, the QB play-actions with the RB, which freezes the LB's for a brief moment, which will delay their underneath coverage. The two outside WR's will run vertical routes, which pulls the 2 CB's and both safeties out of the picture. This leaves an OLB 1on 1 with the slot-WR, running a 10-yard crossing route.
The TE releases off the line to run a shallow crossing route from left to right. The RB releases from the backfield and will cross over with the TE from right to left. The two remaining LB's are responsible for the TE and RB but the MLB drops into coverage to pick up the slot-WR, who is already covered by one of the OLB's. The coverage on the slot-WR is to slow and shallow and the RB is left completely uncovered. The QB elects to target the slot-WR but makes a poor pass despite having solid protection. The pass was actually under thrown and intercepted, though the design of the play obtained the advantage Loeffler was scheming to gain.
Inside look at the WR motion...
The outside WR's motion inside of the slot-WR before the snap, resulted in the CB and safety on that side, swapping out positioning. The CB backs off and the safety cheats up just before the snap. At the snap, the slot-WR runs the vertical route as the motioning WR runs the crossing route. The slot-WR also acts as a pick or shield between the safety and motioning WR.
Imagine Sammie Coates lining up in the slot with a LB or safety covering him on a crossing pattern. Imagine Onterio McCalebb left unchecked coming out of the backfield with 10-15 yards of green in front of him. The underneath routes are stacked over one another, allowing the QB to make a quick read and decision.