I'm sometimes honestly surprised that anybody would shoot on a goalie whose back is turned, or who isn't looking toward the shooter. I mean, sometimes it happens in a game that a shot comes from an angle you don't quite scramble too fast enough. But in practice or warm-ups, it should be basic courtesy (and safety awareness) not to fire off a small, hard chunk of rubber at someone who is not aware of the shot incoming. (padded someone, yes, but not everywhere). I mean, when my softball team practices or is warming up, we don't throw the ball at someone who's not looking.
When I'm at a mixed-age stick time, I do have to remind young kids not to shoot at my back, and not to shoot when someone else is in the lane (the mite age group tends to wander), but like, adults. We should know this.
At the very least, understand that if your goalie is injured, you end up with at best an annoyed goalie, and at worst an injured goalie who cannot play.