In some rec leagues, the referees sometimes have to make a decision on eligibility also, in conjunction with a site supervisor. One city rec league I work, the teams must have the roster finalized by the 3rd week (I think), and cannot add any more players. The site supervisors maintain the rosters, book, etc. If a captain enters an ineligible player in the scorebook, it comes to the referees' attention and we declare a forfeit. Ditto for uniforms. If during pre-game, we determine the uniforms not to comply with league rules, we declare a player ineligible to play that night. Therefore, it is possible that the refs might have to make some kind of a determination during city rec league, depending on the local rules, etc.