Playing out from the back is a numbers problem before it is a technical one. How many forwards the opponent presses with determines how many free players the building team can create.
The arithmetic of the first line
A team building with two center backs and a goalkeeper has three players in its first line. Against two pressing forwards, one of those three is unmarked.
That free player can receive, turn and advance the ball, which forces a midfielder to step forward and creates space behind. The whole sequence starts with the spare man.
Against three pressing forwards the three-versus-three leaves nobody free, and every pass is contested. Building out becomes a matter of beating an opponent rather than finding space.
How teams restore the spare man
The common solutions all add a body to the first line. A holding midfielder drops between the center backs, a fullback tucks inside, or a center back steps wide to stretch the press.
Each solution costs something elsewhere. Dropping the holding midfielder wins the first line but empties the space in front of it, which is where the ball needs to arrive next.
Coaches choose based on which of their players are best equipped for the resulting problem. A team with progressive center backs does not need to drop anyone.
The goalkeeper is the cheapest extra player
Using the goalkeeper as a passing option creates the extra number without removing anyone from midfield. It is the only way to gain a player without losing one.
The cost is risk, since a turnover near the goalkeeper is close to a goal. That risk scales with how far the goalkeeper is from the goal line.
This is why goalkeeper distribution ability has become a selection criterion. A goalkeeper who cannot be pressed changes the arithmetic of every opponent's plan.
Why pressing teams commit a third forward
A pressing team facing a build-up with a spare defender must either accept the free player or send someone to him. Sending a midfielder leaves a hole in the second line.
Committing a third attacking player instead keeps the midfield intact while equalizing the first line. That is the calculation behind front three pressing structures.
The building team's counter is to add a fourth, and the escalation continues until one side runs out of players it can afford to move. The team that runs out first plays long.
Reading the sequence from the stands
Watching a goal kick, count the pressing players and the building players before the ball moves. The difference tells you who should win the sequence.
If the numbers are even, the long ball that follows is a plan rather than a failure. The building team has correctly decided not to play into a contested area.
If a team has a spare player and still goes long, that usually indicates the free player cannot be trusted on the ball. The arithmetic is fine and the personnel is not.