The proliferation of analytics in football has given us many things. For much of the footballing populous, it has put into clear, definable terms what 'good' and 'not good' looks like. With greater empirical clarity, we better understand what makes a particularly talented attacker so effective. Outside of just goals and assists, we're able to highlight players that are doing effective things efficiently- even when they aren't surrounded by players of the same caliber.
Much of that is because many of these actions, specifically for offensively-minded players, are primarily individualistic. While the circumstances in which these players act could always be improved to increase the frequency or effectiveness of said action, a player's ability to execute a cutting pass or incisive dribble is largely down to them. With modern metrics, these actions give them due credit. Allowing players to, at least statistically, reap the benefits of their good work.
Defenders, however, exist in something of a blind spot when it comes to the codification of statistical 'good' and 'bad.' This isn't to say there aren't metrics that help define when a defender is doing something good, just that they're far harder to paint a complete statistical portrait of. Their statistical aberration is also somewhat complicated by the role defenders have been asked to play in the modern game. Fullbacks are all but required to have a fair bit of offensive output given the space they're allowed if the shape and movement of their own side is proficient, while central defenders command near world record fees if they can penetrate central spaces and connect seemingly harmless positions with their offensive counterparts.
In a sense, defending is hard to properly quantify because it's often a collective, almost immaterial action. Kalidou Koulibaily throwing Mario Rui into Kylian Mbappe is, unironically, good defending. I don't think there's a metric to quantify that action.
But, funny, effective defending actions aside, the debate between actions that are immediately quantifiable and not still rages. For example, if a defender is making a lot of tackles per game, that really says more about the positions they're being put in—either of their own accord or by the team—than it does their individual ability. Even something like interceptions can be largely influenced by role and tactics than by the ability of a specific player. That's why any analyst worth their weight will complement analytical or statistical analysis with conclusions forged by film.
If we hone in on the role of a central defender without delving into the attributes of a proficient ball-playing CB, there's little to track that would give us a good idea as to what they're doing well. While there are certainly proxies for good performance, many of these are team-specific. Virgil Van Dijk plays differently at Liverpool than he did at Southampton. He may have even evolved as a player, but the basis of his attributes are essentially the same.
You might be wondering, then, what these intangible defensive qualities may be. Quotes about it being too late if you've made a tackle aside, what any good central defender does in a modern system has more to do with the management of space than it does an athletic tackle or towering header. Most will be more than familiar with the idea that a good portion of today's defending happens at the front. Attackers pressing fiercely and intelligently do more than just provide the occasional opportunity via turnover; they actively limit the opposition's attack by disrupting it at the source. This can't happen without a practiced coordination with the defenders and the line they hold, as the backspace they defend serves as a platform for how effective—or ineffective—the press can be.
Understandably so, a harmonious relationship between defenders that can hold a line is worth a fair bit. Irrespective of team dynamics, having defenders that directly or indirectly manage space can make or break a team. For years, Leonardo Bonnucci and Giorgio Chiellini, occasionally partnered with Andrea Barzagli, have been emblematic of an effective defensive partnership. Utilizing the best attributes of one another's game, the Italian stalwarts have anchored the most prolific period in Juventus' history, with their most recent achievement extending to that of their national side. Under Roberto Mancini, Bonnucci and Chiellini offered a basis from which a young, energetic Italian attack could be effective both on and off the ball.
Facing England in the final, they had their work cut out. For much of the game, Italy did what they'd been doing—circulating possession in a conservative but effective manner, ensuring Bonnucci's ball-playing ability was maximized. Chiellini and the varying company aiding them on the flanks made sure to communicate with one another frequently and in conjunction with the rest of the team so that England enjoyed little transitional space. The only real blip in that being in the second minute when a miscommunication between Chiellini and Emerson as to which run to focus on allowed Kieren Trippier to hit Luke Shaw with a perfect cross. From there, it was business as usual. Though England stymied a bit of Italy's attacking flare, the Azzurri only grew as the game drew on.
To say, as Jose Mourinho has, that Chiellini played every moment of the game without error might be a bit hyperbolic, but it's hard to find a lapse in concentration. Most of the immediate defending that hampered England's ability to progress through the midfield may have been executed by forwards and midfielders, but the basis of that defensive unit was commanded, at least in part, by Chiellini.
To speak more directly to Chiellini's influence, this chart I stole from Statsbomb paints the picture. 5.3 90s aside, if and when the Italian captain ceded the space after being drawn forward by an attacker, he often made sure to stop, be it through interception, tackle, or foul, their intended action. Understanding the value of what attackers intended to do by manipulating his position, Chiellini ensured that if the defensive solidity provided by the organized compactness of his side was compromised, it wasn't going to bear much fruit.
As something of a platonic example of his ruthless approach, Chiellini's most spotlit moment, the one in which he yanks young Bukayo Saka down by the collar of his shirt late in the game, has drawn both respect and ire. With some claiming the violence of the foul should have elevated his punishment to a direct sending off, there's been a fair bit of debate as to whether the challenge warranted greater punishment. While there is some argument around Chiellini's excessive force, those who claim that the sheer cynicality of the foul be enough to warrant a red perhaps miss the careful balance of Chiellini's ability. To have towed the line necessary in playing a relatively high line throughout the game without having been put in a position where he might have to foul cynically more often might not be entirely down to him, but it's nonetheless something that requires experience, understanding, and talent.
With so much of the modern game being set in favor of attacking players, defending has become harder than ever before. To use the very bounds of the game to your advantage is simply what good players do. Cynical, tactical fouls may be frustrating in the immediate moments of their transgression, but the dynamic is fair. Players are limited in what they can do after being carded, especially defenders. For all the frustration that arose from Saka's impediment, there are probably hundreds if not thousands of goals that resulted from the hesitation of an already yellowed defender. To try and further limit defenders by giving governing bodies the ability to adjudicate on intention is to defang an already declawed position.
Modern defending is hard, not just in understanding, but in practice. Appreciating what that entails in a modern context is part of appreciating the game as it exists.