Did hear about stick-in-the-mud (7)
I believe the answer is:
diehard
'stick-in-the-mud' is the definition.
(thesaurus)
'did hear about' is the wordplay.
'about' indicates anagramming the letters.
'did'+'hear'='didhear'
'didhear' anagrammed gives 'DIEHARD'.
(Other definitions for diehard that I've seen before include "One to resist change" , "One who won't accept novelty" , "Person who resists change" , "traditionalist" , "Obstinately conservative" .)