Stupidly popular, shifty type (about 50) (7)
I believe the answer is:
ineptly
'stupidly' is the definition.
'popular shifty type about 50' is the wordplay.
'popular' becomes 'in'.
'shifty' indicates anagramming the letters.
'about' is an insertion indicator.
'50' becomes 'l' (roman numeral).
'type' with letters rearranged gives 'epty'.
'epty' enclosing 'l' is 'eptly'.
'in'+'eptly'='INEPTLY'
(Other definitions for ineptly that I've seen before include "without finesse" , "In an incompetent manner" , "In a maladroit manner" , "Awkwardly, clumsily" .)