Daffodil- You guys used fabulous in a match (or maybe more, I didn't check all of them) and he wasn't paid up. This is on top of trying to get away with having reflecto main the season as well without paying his league fee.
In all seriousness there's a good way RGL can automatically moderate this. ETF2L has a really nice feature where teams have to upload a status screenshot from the match (P-Rec has a setting that automatically takes one of these). The site then automatically OCRs the steamids in the status screenshot and checks them against the steamids of the players on the team. If it's flagged up that someone who isn't rostered (or in this case isn't payed up) played in the match, then the admins get notified and they check if the other team allowed them (and I suppose also if they're payed as a free agent in this league).