Where people get confused with the above rule is when they only see ONE opponent between the attacker and the goal, and commentators are discussing whether the attacker is level with him.
The other opponent is of course the goalie, who is most often standing on his goal line.
The most common mistake spectators make is shouting that an attacker is well onside, when he is already past the goalie with only a single defender to beat when the ball is played to him.
With only that single opponent to beat, he's already in an offside position. Once he touches the ball, the whistle goes.
My best get-out clause (I ref dozens of games every year) is the "interfering with play" rule, which means that if I think a forward is distracting the goalie or is in any way giving his teammates a sneaky advantage by being in an offside position (though he doesn't touch the ball) I blow the whistle.
This effectively takes us back to the 70s when refs whistled if any attacker without the ball strayed past the last outfield defender, but I don't care, I hate the present offside rule, coaches use it to bamboozle officials, instructing players to stray offside and get in the way of goalies even if they have no expectation of getting the ball.
