Our group rides are typically safe but things happen so we get a few crashes a year. I've learned if you crash no ones going to stop which is kind of sad. We had a guy (no one knew him) who was pushed off the road and into the gutter. He was probably inexperienced didn't push back into the guy. Someone was making a pass over the centerline and with an oncoming car he went back over in and forced everyone to the right. At Worlds is we have 2 blind corners that racers rail at 30+ mph. People have been hit there and I make sure I'm not the first in a group making that turn.
The 2 biggest issues I have is in our weekend ride when it splits from a single ride to A and B, riders in the A ride have to be up front or they'll get dropped before it starts so they try to weave through a peloton of 100 riders and we usually get at least 1 crash a season at that spot. It can easily be prevented by neutralizing that area and letting the A riders get up front but that ride has been doing that way for 30 years so its not going to change.
The other is we have a few guys that consistently overlap wheels, they won't listen if someone corrects them. One guy went down three times.