In American or Canadian football, an interception occurs when a forward pass is caught by a player of the opposing team. This leads to an immediate change of possession during the play: the defender who caught the ball immediately assumes the role of the offense and attempts to move the ball as far towards the opposing goal as possible. Following the stoppage of play, if the interceptor retained possession of the ball, his team takes over possession at the spot where he was downed.
Interceptions are predominantly made by the secondary or the linebackers, who are usually closest to the quarterback’s intended targets, the wide receivers, running backs, and tight ends. Less often, a defensive lineman may get an interception from a tipped ball, a near sack, a shovel pass, or a screen pass. As soon as a pass is intercepted, everyone on the defense immediately acts as blockers, helping the person with the interception get as much yardage as possible and perhaps a touchdown; at the same time, everyone on the offense becomes the defense and may attempt to tackle the ball-carrier. (Wikipedia/LA. Times)