Why can't people just answer the question asked? He's asking about an untrained person; not asking for opinions on why training is good (which we all know).
The ANSWER to the (good) quesion asked is probably one of these things, *assuming* a certain fair level of basic strength and agility:
1. Short Spear / Assegai
2. Short ("Chisa"- or "Ko"-) Katana, or other similar 2-handed short sword such as a Chinese War sword
3. Tomahawk / short axe
3. Pepper spray (don't discount this one's effectiveness!)
Those are probably the most effective (and most intimidating, except pepper spray perhaps), but to add a few more that I'd only relegate to the 2nd tier, but which can make fine weapons:
5. Short sword or dirk or kuhkri (1-handed blades)(offhand arm is used to block, balance, etc.)
6. Walking stick, aluminum baseball bat, or other good basic, well-balanced long-ish 2-handed "stick"
7. Taser
Flashlight, ASP type batons, T-handle batons, etc., IMO cannot compare to the effectiveness of these. A long tough flashlight, short baton, or ordinary short fixed blade knife or even folding knife are not terrible options at all, but IMO not as good as these. I'd probably put them in the third tier of preference if my life depended on it.
I guess if I had to choose, I'd go with the long-bladed, short-staffed assegai. Combines the best of: sword, stick, and spear/lance. Chisa Katana or Chinese War sword close 2nd, and among those two, I'd take a Chinese war sword in a larger room, and a 19-20" chisa katana in a small room. Pepper spray 3rd choice for me personally. Taser 4th. The reason the taser is not higher is because it can be more easily defeated with thick clothing or just a miss.
Here ya go:
http://www.kingofswords.com/Swords/Cold-Steel/Cold-Steel-Assegai-Spear.html
http://images.google.com/images?q=c...esult_group&ct=title&resnum=7&ved=0CDgQsAQwBg
http://images.google.com/images?hl=...1&sa=1&q=chisa+katana&aq=f&oq=&aqi=g1&start=0
Please note that for the weaker and older among us, I'd choose pepper spray over contact weapons.