The most powerful addition to an attack has to be a marauding center-back. A player who shows up in places that the opposition would not suspect. You will be able take the penalty box by force.

maraud intransitive verb to roam about and raid in search of plunder

Every player is marked one-v-one. What is the ultimate plus one? A center-back that is not afraid to get forward. One that is encouraged to get forward.

Why does the center-back have to be limited to the back line when, with coordination, the center-back can be used in attack?

No one sees it coming.

If I had to pick one player to play this role, it would be Declan Rice.

A player that is defensively sound and good at winning duels because a maurading center-back will be caught higher up the pitch frequently. A player who is not afraid to make runs through the channels, through the half-spaces, towards the front line. Someone who is tall and fast, a mismatch for the fullbacks that will attempt to follow them. Most importantly, a player that is good at shooting and who will overpower the opposition’s defenders when the ball is crossed into the box.

Everyone is marked one-v-one, and then they go, they go, and one defender has to dismark from their attacker to follow the center-back getting forward.

As long as there is coordination, it will work. And when it works, the center-back is either going to draw a defender away from a forward, they won’t be marked, or the opposition’s forward will mark them.

It is an even bigger mismatch if the opposition’s forward tracks back with the center-back because they usually like to switch off in defense. That is an immediate plus one in attack because they won’t track back with the attacking center-back with the same amount of intensity or urgency.

In moderation, because you want to maintain that level of surprise; in the hyperpositional world of football, a tall, fast, coordinated, marauding center-back who is good at dribbling can become a missile.

It is hard to counter-press aggressively in your own end when that constant threat is there lurking.