A strategy in which an offensive player will switch directions to run back against the flow of play in an attempt to find a seam with which to advance the ball downfield through. A cut back is most effective when a hole appears on the weak side of a running play, and the running back stops and tries to break through that hole. If the defense was too aggressive in their pursuit, there will not be many defenders on that side, and a big gain could result. The downside to a cut back is that there are less blockers on the weak side, and the cut back could result in a loss of yardage.
An athletic running back will use the cut back effectively to gain more yards than a play might normally gain. If the planned direction of a running play gets clogged up, the running back can try to cut back and gain yards on the other side of the line of scrimmage. If it works, it can result in a big gain by catching the defense off guard. The cut back can be risky, since it forces the running back to stop for a moment, allowing the defense an extra second to tackle him.