Boxing trunks are made specifically for boxing. Danna Scott says, “The special cut of the trunks fits a man’s groin protector, and the extra-wide waistband is used as a marker against low blows.”1
While any pair of shorts will do for regular gym work outs, I would suggest spending some time making sure that your competition trunks fit snugly and are comfortable. You don’t want any surprises on fight night. Too often I have seen poor-fitting trunks on professional fighters that lead to distractions. Even a casual fan has probably seen a bout where the trunks begin to either ride up or down the protective cup, and the boxer has to continually bring his hands down to adjust them. This type of distraction can be completely avoided by just spending a little more time trying on the trunks. Nothing could be stupider than getting hit by a punch because you dropped your hands to adjust your trunks.
Boxing trunks these days come in many styles. The traditional two color trunks, with the wide waistband a different color from the actual shorts in order to easily see the legal belt area is always a good choice. If you want to get flashy, you could wear multi-color shiny trunks with all sorts of wacky designs. However, I would definitely avoid wearing anything like Paulie Malignaggi’s “string” shorts, unless you’re a well-respected professional.
1. Scott, Danna. Boxing: The Complete Guide to Training and Fitness. New York: The Berkley Publishing Group, 2000.