As someone who has organized sport groups from small (single weekly pickup games in the mid west) to large (300+ people vying for spots in three games a week in a major city), I've looked into various sport-specific apps. But in the end, I've always come back to Meetup. They used to have more rough edges, but they've gotten much better.
FYI, here are Meetup features I can't live without as a sports event organizer:
- auto-scheduling of games
- option to make RSVP required (drop-ins are just a hassle, b/c then you never know how many people to plan around)
- online payment collection ("Here's my $3" is a waay more reliable indicator of interest/attendance than "I'm in" - this changed everything for us, and covers our facility rental)
- group-wide + member-specific messaging
- an app and account most people already have and are willing to use
Don't mean to sound pessimistic, just sharing thoughts - best of luck!