TCUFrogs said:
So, the player(s) should "wait" until the ball is kicked past them to run ahead toward the goal, and thus avoid advancing past a defender until the ball goes by?
Sorta. Your description made it sound like offsides position was determined by the location of the ball rather than the timing of the pass, but you may understand it.
Just to be clear, a player cannot advance past the last defender until a ball leaves the passer's foot. He can advance past the last defender before the ball goes by the last defender as long as the ball has already been passed. For example, a ball may be passed from midfield to a player on top of the 18 yard box so the player passing the final defender would take less time than the ball traveling 40 yards through the air.
This rule does not apply when the offensive player receiving the pass is behind the ball when it is passed to him. In other words, if the player crossing the ball crosses it from the corner near the flag to a player at the penalty spot it doesn't matter if the last defender is at midfield; the player receiving the pass is onside. This caveat does not apply on corner kicks.
One final caveat that you may never see in a game occurs when the goal keeper is caught too far up field. The offsides rule actually requires that an offensive player be behind the last TWO defenders, but since the keeper is nearly always one of those defenders it is usually taught as the relationship between the attacker and the last defender. In the event that the goal keeper is caught up field, the attacking player must be behind the final two defenders when the pass is kicked to him. As I said, though, I've only seen this called a half dozen times in my life so if you don't watch soccer often you'll likely never see it.