A player’s number exists at the intersection of chance, tradition and personal significance. On the one hand, it’s meaningless: there might be technical meanings attached to numbers like 10 or 1 or 6 in soccer, but there are no hard and fast rules about it. Such associations are easily scrubbed off them. New players are told what’s available and then they make meaning out of them. Christian Ramirez picked 21 when he got to Minnesota United because his wife wore the number 3 when she played in college.
Other players have only vague preferences. They want low, even numbers if they’re defenders or they feel like high, odd numbers don’t sit right, somehow.