Host runs off in very skimpy underwear (5)
I believe the answer is:
thong
'skimpy underwear' is the definition.
(a thong is a skimpy type of underwear)
'host runs off in' is the wordplay.
'host' becomes 'throng' (both can mean a large group of people).
'runs' becomes 'r' (cricket abbreviation).
'off in' indicates named letters should be taken away.
'throng' with 'r' taken out is 'THONG'.
'very' acts as a link.
(Other definitions for thong that I've seen before include "Leather strip fastener" , "Narrow strip of leather - beach garment" , "Skimpy underwear" , "Insubstantial underwear" , "scanty garment" .)