All great teams are formed off a rock-solid base, an impermeable barrier between success and failure.
Defence wins championships, so they say, and a top-class central defender is paramount to any club with aspirations of winning their respective domestic division, or any of the biggest continental trophies.
The role of a centre-back has changed down the years, though, as have the requirements of a top defender in general.
Where once a tough-as-nails, hard-tackling, long-ball-clearing defender who never lost an individual battle would be hailed as a game-winner, now the same abilities have to be significantly added to for a centre-back to be considered complete.
Whether you favour a Paolo Maldini, a Mats Hummels, a Jamie Carragher or a Gerard Pique, the modern defender has to have an element of all about them to be truly looked upon as world-class.
And what of the ultimate, ideal defender for the modern game? One who can lead his team to glory from the back, taking various strengths from a range of players and putting them all together to provide the most complete defender around? Exactly what does a manager or a scout have to look for to find such a specimen?
Having changed so much over the years, it is important to acknowledge the role of the complete defender in the modern game.
While primarily their job remains to clear the ball and stop the danger being created by the opposition against their team, they are far from restricted in the ways that they can approach this job. Not only that, but they are increasingly required to be more than proficient at a number of them.
Just as the top forwards always find the right angle, the right moment to move and the right part of their body to shoot with, so must centre-backs learn to be similarly versatile in their approach to defending.
Indirectly influencing the play has become just as important as directly doing so, but all good players at the back should begin with the defensive staples.
Tackling has long been considered an art form, but now more than ever it is imperative that defenders are masters of this particular area of the trade.
With ever-increasing restrictions on physical contact or even the threat of "overly aggressive" approaches to winning the ball, defenders have to be able to make the right decision to tackle at exactly the right time, just a few times per match.
Statistically, it is rare that a player will make more than four tackles per match in any of the top leagues around Europe, and defenders tend to be more in the three- or four-per-game bracket. It is imperative, then, that they are able to judge just when is the right moment to make their move and also possess the execution to make firm and clear contact with the ball before they do so with their attacking opponent.
Knowing when to not tackle is equally as important. Commit yourself to a challenge and you stand little chance of recovery if the forward bests you; a top defender must be aware enough of his surroundings to understand that at times, the best course of action is to do nothing except hold his position.
If a forward cannot get past him, he cannot find a direct route to goal, and in just a couple of seconds of holding up the attack, a defender can help his team reorganise the defensive line with greater numbers, especially if they have been hit on the counterattack.
While the game of football evolves, so do the basic techniques and requirements of the players within it. Just as players have had to adapt to tackle less often or less forcefully, so has marking during matches seen styles and technique change.
There has been a general disappearance of direct, one-on-one, man marking in open play for central defenders.
Where once centre forwards might have been relied upon to occupy the same positions for much of the match, they are now encouraged to be far more mobile, working the channels, dropping deep and swapping with each other when two play up top together. As such, the role of the defender in marking them has also had to adapt, while it is more common to see a midfielder employed to do a specific man-marking job on an attacking or playmaking threat in the middle of the park.
The central defender is now much more likely to be asked to mark zonally in open play situations. In a traditional back four, the right central defender will look after whichever forward drifts to the left of the attack, and vice-versa.
For the top modern centre-back, he must be able to comfortably take on—and pass along—marking attacking threats for inconsistent periods of time, all the while holding his position in the back line and being able to track the movements of the attacker while not losing sight of the game unfolding.
Often we may hear about a defender “caught ball-watching”; essentially this comes from the centre-back being unable to do exactly the above—maintain focus on the game taking place, while still being aware of the movement in the front line.
Marking and positioning have become inextricably interlinked for centre-backs, and for a great of the modern game it is imperative that they can control the threat of the attacker without causing an imbalance in the defensive line.
On set pieces, on the other hand, zonal marking still fights for dominance in some countries against the long-standing comfort of man-to-man combat.
Some clubs will employ a mix of both; usually the centre-backs and any other proficient headers of the ball will go up against a direct rival, with the explicit aim of winning that one individual battle which could prove the difference between scoring and keeping out a goal.
Other defenders will “mark” space, taking up positions within the penalty area which are deemed likely to be targeted by the attacking set piece.
For the top defender, two things are important with regards to defending these set pieces; firstly the ability to switch seamlessly between man and zonal marking, and secondly the tactical ability and commitment to operate in whichever method his manager deems best suited.
This could change on a game-to-game basis, or it could be a staple repetition within the club; either way the head coach will decide how set pieces are defended, and the great modern centre-back must be able to be effective in either role.
Defending and marking from these set pieces leads us nicely on to perhaps the final major on-the-ball defensive ability that all top centre-backs need—the attribute of heading the ball.
In an era of long throw-ins, cheap free kicks and percentage plays, defenders must at the very least be proficient in the technique of heading the ball clear of danger and possess some level of bravery to go into aerial challenges against an opponent. The top defender will do both with staunch commitment and the knowledge already in his mind that he is going to do both successfully.
Not just technique but also power and force are important in making headed clearances, but there are times when even the slightest glancing header, changing the direction or height of the flight of the ball just a few inches, could turn out to be goal-saving.
A diving header facing his own goal is a peril that most defenders go through at some point in the season, and in building our top-class centre-back we must acknowledge that this is a moment that requires both great care and great commitment.
Not going for that cross could lead to an easy chance for an attacker—but likewise going for it and getting the header wrong could lead to the most dreaded of outcomes for a defender: an own goal.
The modern defender has to use any part of himself to protect his goalkeeper whenever he can, and making blocks on shots is a guaranteed way of getting the fans onside and his teammates relishing his commitment to the cause.
It doesn’t have to be a five-yard slide, smothering a goal-bound shot like a bomb hero, but merely putting his body in the way of an effort. A close-range shot can be blocked by the legs or knees, while a late slide can present a big target for the attacker to shoot past before the goalkeeper has to make a save.
Again, not only physical technique is required here, but much more importantly are the mental factors that go into the split-second decision-making process of the defender; anticipation of the situation, the bravery and determination to go in where it might hurt, and the willingness to stop the shot hitting the back of the net by whatever means necessary.
This mental side of the game is absolutely vital for any top-class defender.
Not just in the moment, when he has to make a last-ditch tackle or brave block, but in every moment during the 90 minutes to make on-going assessments of the game, anticipate where players will pass to or make runs to and being able to process exactly where the danger will come from. He must also do this consistently, game after game, week after week.
A top central defender must always be switched on, alive to potential threats. The very best of them can move across and make an interception even before the danger becomes apparent, before tackles or blocks are even necessary.
There is also the tactical side of the game to consider. A central defender may be asked to play in a back four or could be one component in a three-man centre-back system. The positioning and requirements on the ball in each role can be very different, and it may be that teams opt to switch formations and tactics on a regular basis.
The defender, therefore, needs to be able to adapt to different situations, even if the number of defenders isn’t strictly affected.
Employing a higher-pressing tactic in the wide areas of the pitch, for example, may necessitate the full-backs to hold a much higher line than the centre-backs. In that instance, if a ball is played down the channels, the central player must be able to cover in the wider areas of the pitch.
Often it is beneficial to a centre-back later in his career if, during his formative years trying to break into the first-team, he has spent some time playing at right- or left-back, before becoming a regular in the middle. This gives an appreciation of the position and a level of comfort on the ball and defending in those zones of the pitch.
At other times, a team could sacrifice playing a deep-lying holding midfielder for a more attacking outlook; at that point there will be less protection and more open space in front of the defence. Our top-class defender must have the ability to assess when is the right time to step into that space and close down an attacker, and he must know when to hold his position and invite the attacker.
With so much to do, both mentally and defensively, it is apparent that defenders need to be incredible athletes, just like the rest of their teammates. It may appear that because they have less running to do, perhaps only covering about seven kilometres per game as opposed to the 10 kilometres you can expect from a midfielder, that they can get away with being less primed physically.
Not so, of course. Constant one-on-one battles necessitate a level of agility and core power that some midfielders might never manage, while strength and aggression are also key traits.
Aerially, the ability to head the ball does no good whatsoever if the player cannot get off the ground—so power in the lower leg muscles is imperative also for a good leap.
Physicality and athleticism are absolute necessities for a top modern central defender, who must be able to sprint and have good acceleration for those moments where cover is needed or they must keep up with an attacker in full flight.
The final on-the-ball element, which is required of the modern central defender is an innate comfort and ability on the ball. No longer is merely clearing the ball enough; players must be able to find a teammate 10 or 20 metres away, and be able to recycle the ball constantly in open play.
There are no longer four defenders, four midfielders and two attackers; when in possession and constructing patient build-ups to an attack, the centre-backs must be able to receive and pass on the ball several times. Even the goalkeeper is another option to pass to, and so the centre-back may receive it from him as well.
And when passing is not enough, the centre-back has the element of surprise at his disposal—he can charge forward with the ball at his feet, very quickly covering 20 or 30 metres of ground before the opposition has a chance to re-form the defensive line, and make provisions for his unexpected addition to the build-up or attack phase of play.
The ability to make a good decision with the final pass (or shot) therefore, at the end of this exhilarating run, becomes of paramount importance, as the centre-back will be well out of his own defensive position by this time.
While we mention defenders in the final third, it would be remiss not to talk about the growing expectation that they should be able to contribute to scoring goals.
Particularly from set pieces, a top centre-back who is a threat in the air could reasonably be expected to find the back of the net four times a season, and there are some who do it far more often. Excelling at taking set pieces themselves is not a requirement, but rather an unexpected bonus.
With all these requirements, it is clear that even the very best modern centre-back cannot do it all himself. A defence is, after all, only as good as its central partnership.
The driving run into midfield would be pointless and dangerous if he had not the confidence in his partner to cover the gap he left. A sliding tackle to win the ball would be rendered ineffective if the rest of the defence did not follow up the challenge, and instead a second attacker was left free to bear down on goal and shoot easily.
Constant communication—not always verbal—and an appreciation of the partnership are vital ingredients for any top centre-back, perhaps especially for one so complete as our modern-day world-class prototype, for while he is taking care of all these elements in the game he needs to be reassured that his partner is taking care of his own business.
A great defender must show leadership, must generate organisation and must be rigid in his tactical demands—as imparted by the coach—while being flexible in his approach.
Above all else he must remain professional. Dedicated to the cause of his primary role of defending, he must remain focused in games and he must be reliable, consistent and unbeatable.