What happens with a player that joins a team after a Detectives league has already started?

The player can start earning league ribbons right away by completing Help Wanted tasks. Depending on whether they made the cutoff for competitions (8hrs before the start of competition), they can earn league ribbons that way, as well. If they didn't make the time cutoff, they will have to wait for the next competition. Regarding the league, If they earn at least 10 ribbons that week, they will earn the team's weekly prize.