What is loss of yardage in football?

A loss of yardage in football is when someone on the team holds the football in his/her hand(s)/arm(s) and someone on the other team tackles the person with the football before the person with the football can advance across the line in which the play started.

For example: the team with the football start on the fifty yard line and they need to advance the ball to the forty yard line for a first down. The football gets snapped to the quarterback. The quarterback has two options: run with the football or throw the football to someone on his/her team so the team can attempt to get the ball across the forty yard line. The quarterback notices that someone on the other team is running at him/her and runs backwards to the forty yard line. Before the quarterback has the chance to either run with the football or throw the football, the person tackles the quarterback at the forty yard line resulting in a ten yard loss.