As explained (with diagrams) in our youth football plays article, teams execute the trap run to cause confusion at the line of scrimmage. Instead of having all offensive linemen block straight forward, one lineman will pull behind another to get to his assigned block.

In American football, a trap run or trap play is a run consisting of a defender on the line of scrimmage (either a defensive tackle or defensive end) getting trap blocked by an offensive lineman or back from the opposite (other side of the center) side of the ball.

Trap is a quick-hitting play that’s typically used as a change of pace of outside runs like Buck Sweep or Jet Sweep. It brings physicality, forces interior defenders to deal with a different kind of block, and quickly gets running backs up onto the second level.

Trap is a quick-hitting, downhill run scheme that kicks out an interior Defensive Lineman and is especially effective against an aggressive pass rushing defensive lineman. If an offense has a bruising, powerful Fullback, it can be just as successful as a Spread offense that has a smaller, more dynamic Tailback running Trap.

The general idea revolves around the defensive back line working as one cohesive unit in a straight line. When one moves up, the rest follow suit. If successfully done, it allows the team to trap players universally on the wrong line of the line.