It is common practice to play as a guest player/Sub. 14U has this issue every year due to high school kids. My dd has played on for 5 different teams this year and no issues. Keep in mind they can move up and down age wise , just not NSA with no issues. Example play USSSA 16U on one team and USSSA 14U on a different team. Most coaches want kids to play and get better, if you restrict kids from playing for other teams as a coach, you are cutting your own throat so to speak with many good players. If you understand the rules its pretty easy. NSA, has cut it's own throat and that is why many NSA early tourneys cannot find teams to play, because teams cannot find enough players. Nationals are a different animal and almost every team picks up players.