hehe, you didn't want to waste another good pellet on that Grackle and stepped on its head instead? To me they are not worthy of touching my shoe. Only hot lead will do for them :-) You must 've broken a little more than a wing if it didn't run away. With a broken wing they can still outrun us and hide in thick brush. You probably hit some vitals too.
Good shooting. That's seems like a good size pigeon!