I'm pretty sure the word 'rain' is referring to that stuff that falls from the sky that's wet. Seems to be a regular occurrence in Vancouver.
nailed it, @AdventureGirl! aha
so my position in quidditch is beater aka I throw dodgeballs ('bludgers') at people to 'beat' them
beater-in-the-middle is a drill where we stand in a circle and there's someone in the middle and we throw dodgeballs at them and they hopefully dodge or block them
seeker-beating is more complicated...so the (human) snitch goes on at 17 minutes through the game, the seekers go on at 18 minutes. so then one beater per team generally goes (instead of focusing on chaser play) to protect the snitch from getting caught by the other team by beating their seeker but at the same time not getting beat by the opponents beaters and protecting their own seeker ? and also there's only 3 balls so they may or may not have one.
Great explanation--but still impossible for muggles to understand.