What is the difference between Offside and Encroachment?

Offsides and encroachment are terms used in the game of football. Offsides occur when a defensive player lines up beyond the neutral zone. It transpires when a defensive lineman is in his stance, and his head or arm is past the neutral zone.

Encroachment arises when a defensive player crosses a line of scrimmage before the ball is snapped. When the defense makes contact with an offensive player, this is offsides. The offense can choose to cancel the play and assess the five-yard penalty, and this is called free play.