You guy's may think I'm crazy. I took the pic and tried blowing it up. From what I can determine, it is a hole, since the deer appears to be in good health, things happen in nature. I would take a guess that sometime the previous fall, or maybe more recent, he may have gotten to close to a dominant buck. This could have been inflicted by another whitetail while the little one was trying to get away. Just my 2 cents. Think back, when another buck is chasing another away, they try and hook them in the side.
Anyway, I may be off the base, but it fits.