How do you teach a defensive back to "look for the ball"? He can't have any idea when the ball is thrown. They have to stick with their man first and foremost. A good, well-coached receiver will wait until the last second to put his hands up so as not to clue the DB in that the ball is about to come.
I'm not a coach, but what do you do?
You teach him to watch the receiver, if the receiver turns his head to look for the ball, so should you.
This topic is pretty stupid, mostly because you are talking about a young secondary with few veterans, and even then, some of those vets aren't perfect.
Some of you have blinders on, where you only see and point out the negatives and completely disregard the positives. It's incorrect to say that Pelini's secondary has never been taught to turn around and look for the ball. I guess all those corners and safeties, NFL or not were never taught to look for the ball by either Marvin Sanders, Terry Joseph, that one guy who came before Joseph. Nah, they were all scrub coaches that didn't teach that our secondary.
I've seen our guys this year turn their heads and look for the ball. Are they consistent? no, far from it. But you know what, I bet half the secondaries in the NFL have their moments where they don't turn their heads and look for the ball. And you know what, those guys get called for pass interference.