Knots, or "acorns" as some call them, can be caused by a variety of factors, but most often are the result of bot fly larva infection. These most typically occur on one or more tines, not the main beam, though it does happen. On more severe knots with significant holes or deformation, the knot is usually the result of a physical injury. I've found sheds and inspected harvested bucks that had thorns from crabapple and hawthorne trees still imbedded in the polished antler.
