This is something alot of coachs dont' know and I happen to find this reading through some thing;
Youth Leagues either allow "unlimited substitutions" can "sub" as many times as he or only allow subbing between quarters. If "unlimited substitution" is allowed, you can sub at these times after a goal kick is called for either team, after a goal by either team, after a throw-in is called for your team ,at halftime, and at an injury time-out if the other team replaces a player . You usually cannot sub on corners, or free kicks. Except at half-time or between quarters, substitutions may only occur with the Referees permission.Players entering & leaving the field should only do so at the halfway line. The rules technically say that a player must leave the field first before his sub can enter the field. Many referees don't enforce this in youth games because there is so much substitution. However, if the Ref says "call them off first", this is what he means. Often, midfielders are subbed the most because they run the most
