I'm with Stealthy... even though I don't like mechanicals. It's tough to say what happened. The extra loud WHACK tells me you missed the spot and hit some bone. As far as BACKING out. Most states dictate that a broadhead have a back plane on the blades that is either at a 90 degree from the shaft or less so that it doesn't have a barb effect. They want it to back out or come out in case of a bad hit. EVEN my reveered Thunderheads will come out or the arrow will break off. BUT, if the arrow is in the right place it won't matter... the deer will be dead within 100 yards. You say this would have been your first deer with a bow. Well, when you get several dozen under your belt you'll say, "I screwed that one up". To rephrase... or imply a different meaning... "It ain't the message.... it's the messenger"!!