Belegarth

This question would belong more in the Rules Questions board, but I'd like the general populace to be able to respond:

Why is the minimum javelin length 4ft?

I actually haven't heard a concrete reason for this, but my guess is stability in flight. When you start getting much shorter than 4' or so, I expect that you would see a considerable increase in end-over-end movement when thrown. It seems like a safety issue; we obviously don't want people to get hit in the face with a pommel.