A burly test-playing bumpkin entering (8)
I believe the answer is:
thickset
'a burly' is the definition.
(thesaurus)
'test-playing bumpkin entering' is the wordplay.
'playing' indicates anagramming the letters.
'bumpkin' becomes 'hick' ('hick' can be a synonym of 'bumpkin').
'entering' is an insertion indicator.
'test' with letters rearranged gives 'tset'.
'tset' placed around 'hick' is 'THICKSET'.
(Other definitions for thickset that I've seen before include "sturdy" , "Solidly built; stocky" , "Compact" , "positioned close together" , "Solidly-built" .)