Wrestler Tighty Whities Are Wrestlers Supposed To Wear Underwear Under Their Singlet?

Are wrestlers supposed to wear underwear under their singlet? - wrestler tighty whities

I am new to the fight, and I do not know if it's normal wear underwear under his shirt. I have a pair of underpants at home, because I wear tighty whiti, but I wear underwear under my shirt, or is the usual practice to go without them?