There might've been a Eagle, falcon or hawk in the area they were trying to drive away from their territory and any younger ones in the flock. Could also be a raccoon etc going after a nest.
Someone in the neighbourhood might've been harassing the crows causing them to raise the alarm.
Crows are a wonderful alarm system for the neighbourhood to let you know something is wrong be it a natural predator in the area or a baby bird, alive or dead, on the ground.
Avoid biting when a simple growl will do
The Spirit Lives As Long As Someone Who Lives Remembers You - Navaho Saying
Vindication ~ For all those pets who became sick or lost their lives from tainted pet food