Yesterday, Michael Cox, author of the Zonal Marking blog and The Mixer, tweeted:
Top marks for England’s squad numbers. Sterling makes sense as 10. Right-backs being 2, 12 and 22 is exceptional. Vardy the right type of striker for 11 with no proper left-winger in the squad. Young 18, Rashford 19, Alli 20 same as for clubs. 13 and 23 keepers. Textbook.
— Michael Cox (@Zonal_Marking) June 4, 2018
Now, there is some science to how football shirts are numbered. I had touched upon it in a very similar post I had written four years ago. You can also read this account on how players are numbered. And if you’re more curious about formations and their history, I recommend you read Jonathan Wilson’s Inverting the Pyramid.
To put it simply, number 1 is reserved for goalkeepers. Numbers 2 to 6 are for defenders, though some countries use either 4, 5 or 6 for midfielders. 7-11 are usually reserved for attacking midfielders and forwards, with 9 being the “centre forward” and 10 being the “second forward”.
Some of these numbers are so institutionalised that the number is sometimes enough to describe a player’s position and style. This has even led to jargon such as a “False Nine” (a midfielder playing furthest forward) or a “False Ten” (a striker playing in a withdrawn role).
There is less science to the allocation of shirt numbers 12 to 23, since these are not starting positions. One rule of thumb is to allocate these numbers for the backups for the corresponding positions. So 12 is the reserve goalie, 13 is the reserve right back and so on(with 23 for the squad’s third goalkeeper).
So how have teams chosen to number their squads in the FIFA World Cup that starts next week? This picture summarises the distribution of position by number: 
There is no surprise in Number 1, which all teams have allocated to their goalkeeper, and numbers 2 and 3 are mostly allocated to defenders as well (there are some exceptions there, with Iran’s Mehdi Torabi and Denmark’s Michael Krohn Dehli wearing Number 2 even though they are midfielders, and Iceland midfielder Samuel Friojonsson wearing 3).
That different countries use 4, 5 or 6 for midfielders is illustrated in the data, though two forwards (Australian legend Tim Cahill and Croatia’s Ivan Perisic) puzzlingly wear 4 (it’s less puzzling in Cahill’s case since he started as a central midfielder and slowly moved forward).
7 is the right winger’s number, and depending upon that position’s interpretation can either be a midfielder or a forward. 8 is primarily a midfielder, while 9 is (obviously) a striker’s number. Interestingly, five midfielders will wear the Number 9 shirt (the most prominent being Russia’s Alan Dzagoev). 10 and 11 are evenly split between midfielders and forwards, though two defenders (Serbia’s Aleksandr Kolarov and Tunisia’s Dylan Bronn) also wear 11.
Beyond 11, there isn’t that much of a science, but one thing that is clear is that Cox got it wrong – for it isn’t so “textbook” to give 12 to the reserve right back. As we can see from the data, 20 teams have used that number for their reserve goalies!
It’s like England has put their squad numbers into a little bit of a Mixer!