Well, a crossbow is a bow, and it can be made primitively, and it does the exact same thing a hand bow does, shoot arrows and kill things. Maybe one issue some have with the crossbow is that is is more a war weapon than a hunting weapon, but crossbows have been used to hunt, I would guess, since the first one was built. And the English Warbow was primarily a war weapon, but those get consideration for BOM.
Not many get built by board members, though. I can only recall two right now I've seen, the current one and one Ivar made a while back, so a crossbow catagory would almost always be empty.
Dane