You can't tell from the TV feed. You have to see the all-22 film or be at the game and decide to watch the defensive backfield to tell.
NFL D's play games with their safeties a lot in an effort to trick the QB and get a pick.
I'm seeing more CFB D's doing it. Especially tOSU v Texas.
what to look for: the D presents a "cover 2" look to the QB pre-snap. In cover 2, imagine each safety positioned on each hash mark, about 10 to 15 yards deep.
Pre-snap, the QB might think, "ah, this is middle field open. D is playing zone, with each safety covering half of the field."
Simplistic, but reasonably one of a few things a QB is discerning with the pre-snap read.
But on the snap, let's say the QB looks to his right. So the safety to that side does NOT back pedal. Instead, he holds his ground and looks to protect the area where a playside WR might be running a deep in/dig/wrap route, or a backside TE or WR might be running an over route. That safety that holds still or even moves down towards the LOS is called "robber" or "lurker" or "bandit".
Meanwhile, the other safety rotates back at a 45 degree angle to cover the deep middle, taking away the big post.
Given how many completions Ucla gave up last year (and this year v UNLV) in the 15 to 20 yards downfield between the hashes (which is exactly the zone that the lurker would be lurking), I don't think Ucla is "rocking and rolling" its safeties.
Maybe it should consider that wrinkle.