you can pass the ball past the last defender, but that defender has to be even with the recepient of the pass when the passer initiates the pass. If the recepient sprints away from the defender after the pass is kicked and receives it, he can easily find himself on a breakaway. Also it doesn't matter where the defender is...if the recepient is in the middle of the field, and the only defender between him and the goalie is up at the top of the field and nowhere near the recepient, it's still onsides.