The third man run is one of maybe five patterns that appear in every good team in the world, regardless of league, style or era. It's also described in coaching literature with a level of abstraction that makes it sound far more complicated than it is.
So here it is without the vocabulary. Player A has the ball. He passes to player B. Player C, who was not involved in that pass, runs into space and receives from B. That's it. That's a third man run. C is the third man.
The whole thing turns on one detail: C starts moving while the ball is travelling from A to B, not after B has received it.
Why it works
Defending is fundamentally about looking at two things — the ball and your man. When the ball moves, everybody's eyes and body orientation move with it. That's not laziness, it's necessary; you have to track the ball or you'll be beaten by it.
The third man exploits exactly that moment. While the defence is adjusting to the A-to-B pass, C is already running. By the time the defenders have processed the new ball position and gone looking for their men, C is five yards past where he was and moving into a space nobody is watching.
Five yards doesn't sound like much. Against an organised defence it's the difference between an easy pass and an impossible one.
The most common version
You'll see this maybe fifteen times in any professional match.
Centre-back has the ball. He passes into the striker, who has dropped deep and has his back to goal with a centre-back tight behind him. The striker can't turn — he's not meant to. He lays the ball off first time to a midfielder arriving from behind. That midfielder was running as soon as the pass into the striker was played.
What's happened is that the striker's job was to be a wall, and to drag a defender out of position by being one. The actual attacking move is the midfielder's run, which started before anybody was looking at him.
The reason this beats a direct pass from the centre-back to the midfielder is that the direct pass is visible and can be intercepted. Routing it through the striker changes the angle, occupies a defender, and lets the receiving midfielder arrive at speed rather than standing still.
The version that beats a press
Under a high press this pattern becomes essential rather than optional.
Goalkeeper to centre-back. The opposition winger presses the centre-back. Centre-back plays into the full-back on the touchline — a pass that looks like it's walking into a trap, because now the full-back has a presser arriving and the touchline behind him.
But the full-back was never going to keep it. He plays first time, inside, to a central midfielder who started running the moment the ball left the centre-back. That midfielder receives facing forward with the entire opposition press now behind him, because they'd all committed to the wide area.
Three passes and you've eliminated five players. It looks like magic on television. It's a rehearsed sequence and every top team has it.
What goes wrong
Almost always the timing, and almost always the same error: C waits.
The instinct is to see whether B controls the ball successfully before committing to a run. It feels responsible. It's fatal, because the whole advantage comes from moving during the pass. Wait for the control and the defence has already reorganised, and now you're running into a space that's occupied.
The second failure is B taking a touch. If B controls and then looks up, the third man's run has already been and gone. B has to play first time — which means B has to have looked before receiving and already know that C is coming. That's the scanning habit again, and it's why this pattern is so hard to install in teams that don't check their shoulders.
Third failure, less discussed: C runs to the wrong place. The run should be into the space behind the defender who pressed A, not just forward. If C runs straight ahead he's running into whatever cover exists. If he runs into the vacated space, there's nobody there by definition.
How to actually train it
Passing patterns with cones will teach the shape and none of the timing, which is the part that matters. I'd avoid them beyond a couple of minutes of introduction.
What works is a small-sided game with a scoring rule: a goal counts double if the assist came from a first-time pass. That's it. Within a few sessions players start looking for lay-offs and start running early, because running late means the lay-off isn't available and the double goal disappears.
The other useful constraint is a game where the player who receives the ball cannot pass back to the player who passed it to him. It sounds arbitrary but it forces a third option to exist on every single pass, which is exactly the habit you're after.
Where it shows up outside possession football
One last thing worth saying, because the third man run gets filed under "possession play" and it belongs to everybody.
Counter-attacks use it constantly — carrier draws a defender, plays wide, wide player crosses first time to a runner who started forty yards back. Set pieces use it: short corner, lay-off, delivery from a runner arriving. Long-ball teams use it: knock-down from a target man to a midfielder arriving at pace, which is a third man run even though nobody would describe it that way.
It's not a style. It's a way of using the moment when the ball is in the air and the defence is briefly blind. Every team can use that moment, whatever else they do.