> activities suggested by r/Syracuse like volleyball ... require you to already have friends.

False! Find a gym with open hours and just show up! I used to do this all the time with my friends, but there were always a few people there on their own. There is always someone a couple players short for their team, so just ask around ("Hey, you need anyone else on your team?") and you'll find some people to play with. Keep coming back week after week and you'll make some friends eventually.

I assume this works equally well for most team sports that can be played casually such as basketball, soccer, and others.