For a team rosters, when it is open, others can request you join a team.
For a closed roster "only the captain can add players." Would it be possible to expand that to also allow the coaches the ability to add players to their team? (You probably already thought of this for your youth league improvements.)
Expand Coach Control
Re: Expand Coach Control
I believe that coaches already do have this ability, it's just the wording that needs to be updated. There are indeed a number of such places that will be reviewed in the youth sports project; coaches are almost never used in adult leagues to date, so they don't get much mention anywhere, but they effectively have the same permissions as captains.