As a running back you must have vision and very good patience. Not to mention quick feet.
You must look over the defense before the ball is hiked and notice different tendencies on the defense.
While observing the defense you must read how many lineman and linebackers are to determine what gaps will be exposed to the offense to make good runs. And the major key is to read the safeties they're the last men on the defense to get passed to score a touchdown. The safeties will show you the coverage they're in rather it be zone or man coverage
There are 3 main different types of zones. Cover 2, 3 and 4. The number of the zone is how many players that are covering the deep pass. And then there is man defense and everybody has one person to guard and get passed
Through out the game they will switch up their defense so major key to the game as a running back is to read the safeties