the straight down kind of shots are a no no. You're margain for error is none and if you're really lucky u may hit spine. It's a shot you just dont take regardless of crossbow or compound. Usually if ur shooting straight down you are going to hit a little above where u aim from the arrow rising. Hopefully the deer survived to be hunted another day. I have never taken that shot but i have helped track deer before that were taken with that shot. It's way to risky and it's one you pass up. Let the deer walk out away from you a short distance and you stand a much better chance of a clean kill. Hope i was of some help.