Do you mean wrestlers? Any boxer I've seen in the ring wears the very long, very baggy shorts with the very thick waistband. They wear them high and they always seem to be made of the shiny nylon material in bright colours - kickboxers tend to have even longer shorts with wider legs - usually with motifs on the shorts. These are sold in any proper sports shop.
Wresters on the other hand... tighter the better as far as I can gather. I'm sure there's someone here who'll be able to explain it but perhaps it all adds to the 'showmanship'?!