Chelsea's latest multi-million pound signing has been the subject of much hot air this January. Ben Shave provides the substance.

It is a sight to frighten even the most seasoned football fan, whether they follow Chelsea or Chester. It invokes all manner of unpleasant memories, most of which end with the ball in the net and a multitude of heads in hands. I am of course referring to the 50/50 through ball. Whether looped high over the top or sprayed beyond the last man, dealing with them with the minimum of fess is essential to the art of good defending. By its very definition, the 50/50 ball is tricky. The propensity for an efficient smothering of danger is equal to that of an acutely embarrassing, game-changing error. Unhappily (from a defensive perspective at least) the average match yields a fairly large number of 50/50 balls, and defenders are judged on their ability to deal with them. No one said football was fair.

I said that it was a sight to frighten fans. But for supporters of Sport Lisboa e Benfica, these normally traumatic moments have, since 2007, been a little less worrisome. And it's all down to a man with hair (think Sideshow Bob, but more layers) that doesn't exactly imply a solid presence at the heart of the back line. A playmaker yes, a reliable centre-back no. But David Luiz, who this evening finally ended the most protracted transfer saga of the window; joining Chelsea for a fee that could rise to £21.5 MN plus Nemanja Matic, is a rare breed: he's perfectly comfortable with 50/50 balls. Indeed, during Benfica's title-winning 2009/10 season, it was not uncommon to see Luiz – with an opposition attacker breathing down his neck – to either drop a shoulder before dribbling smoothly away from trouble, or, when he was feeling particularly calm, perform a Cruyff-esque turn and glide upfield, drawing Olés from the delighted crowd. They were a remarkable display of confidence from a player who only turned 23 last April, and for whom Chelsea is only his second European club.

But then confidence has, of late, become a largely marginal issue for Luiz, who arrived in Lisbon on loan from Esporte Clube Vitória in January 2007, replacing Richardo Rocha. His debut came at the deep end, against Paris Saint-Germain in the UEFA Cup, alongside a fellow Brazilian in Anderson. Benfica lost, but Luiz impressed coach Fernando Santos enough to ensure that he was an ever-present during the final ten matches of the campaign, which saw the Eagles finish 3rd, missing out on the title by just two points in what was the closest finish to the Liga in recent memory.

Although it was a collective failure for the Lisbon giants, Luiz himself made a profound impression, showing admirable composure in what was a pressure-cooker environment. An injury to Luisão meant that the youngster made just his third start in European football in Portugal's most important fixture – the Clásico against F.C Porto, which ended a 1-1 draw. His performances earned him a five-year contract at the Estádio da Luz, and the bestowing of a immense levels of expectations. Benfica had, since the decline of Argel and departure of Hélder Cristovão, lacked a partner for Luisão, and Luiz was installed as the heir apparent.

However, the off-season was to prove a turbulent moment in Benfica's turbulent history. Having seen the sale of his captain and top scorer Simão to Atlético Madrid, relations between the board and Santos were already strained, and when the opening day yielded a poor 1-1 draw at Leixões, the coach was relieved of his duties. His replacement, José António Camacho, used Luiz sparingly, as a combination of injury and Camacho's team preferences reduced Luiz to a peripheral role.

The youngster was sidelined for Camacho's final match in charge (another poor 1-1 draw, this time at home to União de Leiria), and also missed the remainder of the season, which saw Benfica limp home to a 4th-placed finish in the Liga under temporary coach Chalana. Luiz didn't make his return to competitive action until November 2008, by which time the Eagles were under the stewardship of Quique Sánchez Flores.

The arrival of Sidnei meant that Luiz spent much of the 2008/09 campaign deployed as a left-back by the Spaniard, a position where he acquitted himself largely well, lifting his first winners' medal in the form of the Carlsberg Cup. The season however ended in disappointment once more, as Benfica finished 3rd, eleven points behind Porto. For Luiz, it had been a steady but unspectacular second season in Lisbon, although his fortunes should (with hindsight) perhaps be considered in the wider context of what was a transitionary period at the Luz.

2009/10 was the breakthrough campaign for Luiz. The arrival of Jorge Jesus from Sporting Braga presented an opportunity, and the Brazilian grabbed it with both hands, missing just a single Liga match (through suspension) as Benfica romped to the title, playing some of the finest football seen in Portugal for many a year.

It was during this time that his qualities as a centre-back emerged: blessed with an intuitive ability to read the game, noticeable positional sense and deceptive physical strength – which earned him a dozen bookings. Despite the lightweight reputation some of his compatriots are saddled with, Luiz does not shy away from physical confrontations – indeed one of his weaknesses is a sight tendency to give away silly fouls. It was that strength, combined with the characteristics mentioned above, that would have first brought him to the attentions of scouts from European football's major players.

Of course, the last centre-back Chelsea imported from the Portuguese Liga was Ricardo Carvalho, who arrived on the golden horse that José Mourinho rode in on. However, it would be unfair to expect similar performances to Carvalho's – at least at first – from Luiz. Carvalho arrived at Stamford Bridge a Champions League winner, aged 26 and with eight years of experience at F.C Porto behind him. Luiz' European experience is limited, and his sole taste of the Champions League came last autumn, where Benfica were eliminated at the group stage, following a series of insipid displays. He will of course be cup-tied in Europe's elite competition for the remainder of the season.

Furthermore, Luiz remains a work in progress – his disastrous performance against Porto in the 5-0 hammering endured by Benfica earlier this season (where he was given the runaround by another rumoured Chelsea target in Hulk) indicated that left-back is certainly not a position where he feels comfortable at the highest level, as has been erroneously mentioned in the UK press during the saga that preceded his arrival at the Bridge. Benfica have been unable to match the heights of 2009/10 this time around, and Luiz' form has suffered accordingly. There is also the obvious caveat that whilst performing well in the Portuguese Liga is a sign of potential, the step up to the Premier League, both physically and mentally, introduces a plethora of new demands, no matter how talented the player in question.

Football is not, and never has been, an exact science, and no amount of praise from scouts and long-time observers will ensure that Luiz is a success in England. He arrives at Chelsea on the cusp of what increasingly appears to be a transitional period for the club, with his competitors for a centre-back role all (with the exception of Jeffrey Bruma) older and more experienced than him. Patience, not always a virtue closely associated with the Abramovich regime, will be required. The presence of Alex and Ramires will provide a measure of comfort, with the latter in particular a companion from his finest hours as a professional footballer. Yet there is little doubting that despite his pedigree, this is still something of a gamble for both club and player. Chelsea supporters would be well advised to observe how Luiz deals with his first 50/50 ball. Then we'll know more.

As well as co-editing and writing for IBWM, Ben runs his own blog on Portuguese football, Cahiers du Sport. You can follow him on Twitter @cahiers_dusport.