Rick is correct. Rule 4-1-1 States a suitable undergarment shall be worn when tights are not worn. There is a little bit if interpretation that goes on here and its left at the discretion of the ref. Here is my point of view. To me a suitable undergarment is one that would not cause the singlet to be excessively baggy. So if you had a very tight fitting pair of boxers similar to biker pants that did not extend below the 4 inch required inseam of the singlet I don't see any problem with that. So called "tighty whities" would be the prefered undergarment, or a jock strap if you prefer (and I can't imagine anyone that would!). I have seen wrestlers who wear these things called "boxer briefs" they are a hybrid of the two they are shorter in the legs than a real boxer and they fit close to the skin, and they are acceptable. But no you can't go commando for sure, and if you have baggy boxer shorts they are unacceptable as well, it presents a danger of getting ones fingers broken. I can't believe someone actaully went out and wrestled with no undergarment I find that amusing.