FourFourTwo's (not entirely serious) guide to squad numbers
Back numbers in football - meaning and history
The History of Numbers
When did football jerseys start having numbers at the back? - Quora
Squad number (association football) - Wikipedia
Best Player for Every Number in NFL History
NFL jersey number updates: Tracking which NFL players wear No. 0
The greatest players to wear each shirt number in football
Soccer positions explained: names, numbers and what they do
Shirt Number Stories: No. 77 - AS Roma
A look at the Netherlands' European Championship numbering
History Of Squad Numbers In Soccer, and How They've Evolved
A look at the Netherlands' European Championship numbering