A combination across three players: the first pass goes into a marked second man, he lays it off first time — and the ball arrives at a third man running from deep.
Against a compact opponent the direct route forward is nearly always blocked. The third-man combination gets around it by occupying attention: the passer and the second man pull the back line's eyes towards them while the third man starts from their blind side and is only spotted once the ball is already travelling. Everything hangs on timing. Start too early and the third man is offside or clogs the space himself; start too late and the gap has closed. The run begins at the exact moment the second man lays the ball off — which means you must have seen the gap earlier with a shoulder check, not gone looking for it while the ball is in flight. A common misconception is that this is elite-only equipment for breaking down low blocks. It works even more easily against aggressive pressing, because there the opponent pulls his own line apart for you.