Daniel Austin
BBC Sport elder journalist
Trent Alexander-Arnold wore the fig 66 astatine Liverpool, but La Liga rules forestall him from doing truthful astatine Real Madrid.
Spanish top-flight clubs indispensable sanction a 25-man 'A' squad astatine the commencement of each season, and each subordinate included is obliged to deterioration a fig from 1-25, with goalkeepers allocated the numbers one, 13, and 25.
Youth players not included successful the archetypal 'A' squad tin deterioration higher numbers.
At the clip of Alexander-Arnold's signing, the lone outfield numbers disposable betwixt 1 and 25 were 12 and 18, and the England planetary opted for the former.
Real's fig 12 was antecedently worn by France midfielder Eduardo Camavinga, but helium switched to fig six a twelvemonth agone aft the departure of Nacho Fernandez.
Prior to that, it was worn for 16 years by Brazilian left-back Marcelo, who won 25 large trophies during his clip with the club.
Former Bolton defender Ivan Campo besides wore that fig during his four-year stint astatine the Bernabeu.
Why did Alexander-Arnold deterioration 66 astatine Liverpool?
Alexander-Arnold wore the fig 66 garment connected his Liverpool debut - against Tottenham successful the EFL Cup successful October 2016 - and ne'er switched.
The full-back had nary idiosyncratic transportation to the fig - it was simply allocated to him arsenic a youngster.
But adjacent erstwhile helium overtook Nathaniel Clyne to go the Reds' first-choice right-back, helium opted to instrumentality with 66.
Image source, Getty Images
Alexander-Arnold played 354 times for Liverpool wearing the fig 66 shirt
Liverpool kit co-ordinator Lee Radcliffe told the club's website: "When we get immoderate young lads that travel down from the academy, we ever deliberately effort to springiness them a high-ish number. We don't similar to springiness them a debased fig successful lawsuit they deliberation they've made it consecutive away.
"When you spot him present lifting trophies and celebrating with No 66 connected the back, it's a weird feeling and I can't truly picture it. It's weird to spot specified a precocious fig and for idiosyncratic to beryllium blessed with it!
"Obviously Trent's got rather attached to the number."
Alexander-Arnold is not the lone existent England subordinate to person a precocious squad fig aboriginal successful their vocation and persist with it.
Both Declan Rice (41) and Phil Foden (47) person maintained the garment numbers with which they made their nonrecreational debuts.
Why won't Alexander-Arnold usage his surname connected his Real Madrid shirt?
Real person besides revealed Alexander-Arnold volition deterioration the sanction 'Trent' connected the backmost of his shirt.
Using a archetypal sanction alternatively than a surname connected the backmost of a garment is not uncommon. Players including Alexander-Arnold's erstwhile team-mates Virgil van Dijk and Darwin Nunez usage their archetypal name, arsenic person others including Dele Alli, Sergio Busquets, Memphis Depay, James Rodriguez, Alexis Sanchez and Jobe Bellingham.
Alexander-Arnold has not explained the reasoning betwixt dropping his surname, but has besides altered his Instagram grip to conscionable his archetypal name, indicating the determination is astir his wider idiosyncratic brand.
Use of a mononym - peculiarly 1 which is reasonably unsocial - is often seen arsenic a spot successful branding and merchandising arsenic it stands retired and is easier to remember.
Mononyms are often utilized arsenic portion of a branding strategy by endowment agencies who negociate singers, actors, and different high-profile nationalist figures.
Do different large European leagues restrict squad numbers?
La Liga is not unsocial among Europe's apical 5 leagues successful restricting the squad numbers players tin take from.
The Bundesliga requires first-team players to deterioration numbers from 1-40. If a squad uses much than 40 players successful a season, squad numbers should beryllium assigned consecutively from that constituent onwards.
The Premier League, Ligue 1, and Serie A don't person restrictions beyond allowing players to take from 1-99.
Before 2022, Ligue 1 did besides person a regularisation - mandating that players usage numbers 1-30.
Serie A has besides relaxed much stringent rules, though 1 it has maintained is simply a prohibition connected the fig 88, which is sometimes utilized successful Italy to show enactment for fascism.
High squad numbers are overmuch much communal successful Serie A than the different apical 5 European leagues - successful the 2024-25 season, each nine speech from Juventus had astatine slightest 1 first-team subordinate utilizing fig 80 oregon higher, and 8 clubs had a subordinate wearing fig 99.
Image source, Getty Images
Cameroon midfielder Frank Anguissa, formerly of Fulham, present wears the fig 99 for Serie A champions Napoli
What astir different antithetic garment numbers?
When Brazilian goalkeeper Rogerio Ceni - a prolific scorer of free-kicks and penalties - broke the quality grounds astatine Sao Paulo successful 2005, helium wore a commemorative garment bearing the fig 618 to people his tally successful an authoritative lucifer against Atletico Mineiro.
In 2010, an administrative quirk meant Australia midfielder Tommy Oar became the archetypal subordinate to deterioration a three-digit fig successful an authoritative planetary fixture. The erstwhile Utrecht subordinate made his planetary debut wearing fig 121.
Moroccan striker Hicham Zerouali was allowed to deterioration the fig 0 astatine Aberdeen successful 2000 aft fans nicknamed him 'Zero' - but the fig was banned for the pursuing season.
Though the fig 1 garment is traditionally worn by goalkeepers, immoderate outfield players person worn it, including the Netherlands' Ruud Geels astatine the 1974 World Cup, Ossie Ardiles for Argentina astatine the 1978 edition, and erstwhile Juventus and Barcelona midfielder Edgar Davids during his 15-month spell arsenic player-manager of Barnet.
Image source, Getty Images
Rogerio Ceni scored 129 goals successful 1209 matches crossed a 25-year career, contempt being a goalkeeper
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