Ok, soccer (and Rugby) are just mobs running around randomly. Don't try to pretend they have positions. REAL Football does have positions (Quarterback, Half back, etc.), and numbers like 0-19 for quarterbacks. Which of course, has NOTHING to do with Blood Bowl. In my league, only myself and one other coach have ever even been to a RL football game. The rest never played in a kid's organized football league (MY glory days!), never saw their friends or sibs play, never went to high school games (I was too slow and really only lacking both talent and desire), or college games(hah!), or any pro game. Probably never watched one game on TV, or got invited to a Superbowl party (OK, at the parties, my wife hardly watches the game). None of which is relevant, but where do we get such men?
What is relevant to BB is a way to identify each player in their identical uniforms. Typically, the model is modeled after its position (Throwers modeled throwing a ball). Which is why positions don't have a designated range of numbers. But, to keep track of players for league purposes (advancements, injuries), numbers do the trick. Either decals, or sharpie numbers on the base.