If the defender is on the opponent's half of the field and is closer to the opponent's goal line than both the 2nd last opponent and the ball, then they are in an offside position and can be called for offside.
Neither the attacker's nor defender's arms are included when judging offside, because they cannot be lawfully used to play the ball.
The signal for offside in soccer is when the lineman raises his flag above his head and stops running in line with the last defender. When the referee has realized the linesman has raised his flag the linesman points the flag out in front of him.
A player is in an offside position when they are on the opponent's half of the field and closer to the opponent's goal line than both the 2nd last opponent and the ball. If is not necessarily an offense to be in an offside position.
Its called Offside, or being in an offside position. Being in an offside position, in and of itself, is not a foul. The foul occurs when the ball is PLAYED to the PERSON in an offside position. You can be "passive", not involved in the play, in an offside position and there is no foul.
A defender in soccer moves up when the ball is close to the oposite net. If a striker from the other team stays back, one defender should stay to cover him. You could also try to make him offside by stepping up, but not past the halfway line.
The attacker's offside status is not reset by a mere deflection off a defender. A team mate of the attacker need only touch it. A defender must control it.
The offsides rule in soccer prevents a player from standing by the goal and waiting for passes. When the ball is kicked, you cannot be behind the last defender (not including the goalie).
should be the attacker but usually the defender
You can't.
A player CAN NOT be called for an offside infringement if not "active in the play" however you can be "active in the play" without playing the ball. A player CAN be in an offside POSITION with out being "active in the play."
You can avoid being called offside by staying in an onside position until you have possession of the ball. If you are caught offside, you can avoid getting called and penalized by staying away from the play and not becoming involved. If is not an infraction to be in an offside position, unless and until you are involved in the play.
If the player receiving the ball is behind, or level with, the penultimate (second from last) defender when the ball is played, there is no offside. If the player receiving the ball is behind, or level with, the ball at the moment is is played, there is also no offside infraction. But, if the player receiving the ball is ahead of both the ball and the penultimate defender, and is not on his own half of the field, then the offside infraction must be enforced.