May a field player have number one in soccer?

Answer 1

From the text of the official IFAB Laws of the Game as published by FIFA, there is no indication that any player may or not wear a certain number. In fact, there does not appear to be any requirement that players wear numbers at all.

Each association or other governing body under the auspices of FIFA may set their own rules regarding the numbering of jerseys. In most, there is no requirement for a player in a certain position to wear a specific number, though many competitions limit the range of numbers that may be employed, typically between 1 and 23 (the maximum squad size).

By tradition, goalkeepers usually wear number 1, a secondary GK will wear 12, 18, or 22, and a third alternate GK will often wear number 30 or 33. A team captain often wears number 7, but all of this is by tradition, not by rule.

Answer 2

There is no requirement that a player have a number in the Laws of the Game. The competition authority decides any numbering rules.