Sometimes, a wide receiver can make a dope block on the outside to spring a running back for a huge play. They can fight and fight their defensive back downfield, ensuring they can't break free to make a play on the runner with the ball.
Or, as Oklahoma's Dede Westbrook found out here, the wide receiver can just pretend he's running a passing route and hope the defensive back buys it. Oklahoma State CB Michael Hunter did, just running downfield oblivious to the fact that Samaje Perine was sprinting behind him en route to a 68-yard touchdown.
Westbrook hit Hunter with a believable move at the line of scrimmage, and Hunter bought it, hook, line, and sinker. He didn't turn around until he was at least 40 yards downfield, and at that point it was too late. There was no safety on Hunter's side of the field, so he was really the only person capable of stopping Westbrook once the play got outside. And it got outside. The touchdown made the score 14-10 Oklahoma.
Let's break this down moment by moment. (All screenshots via that ESPN video.)