Don't believe there are any regs around players being between seniors and U17s are there?
34 PLAYER REGRADING
34.1 A registered player can play in any team entered by their club, in any league, of any competition at the discretion of their club, if the re-grade and eligibility rules are followed.
34.2 A player will be automatically graded to the team they play their first competition game of a new season for.
34.3 Named substitutes who do not take the field, are not graded to the higher team.
The intent of the above regulation is to allow players to be named as a higher-grade substitute, but still play lower in the grades without being considered a re-grade.
34.4 Player regrade rules do not apply between different competition types (Men’s Leagues, Women’s Leagues, Masters League, Junior Leagues etc.)
34.4.1 Dispensation and Player Eligibility criteria still apply.
34.5 A player can only be re-graded once during any one week, including Easter and Queen’s Birthday weeks.
34.6 Failure to comply with these regulations will result in a 3 – 0 win to the opposing team.
34.7 Capital Development Leagues
34.7.1 Up to four players in total can be re-graded down from a Capital Development League team per matchday:
a This must be to the club’s next adjacent team.
34.7.2 Any player who reaches 66% of league matches for any one team cannot re-grade down again to a team in a lower division for the remainder of that season.
34.7.3 No player can be re-graded within their club following conclusion of their current team’s matches. This regulation applies if the league they are entered in is unfinished.
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Oh wait- just clicked that the issue was they played for a different club? That's a bit of a different issue.