Nan: she nags, I suspect, creating mischief (11)
I believe the answer is:
shenanigans
'mischief' is the definition.
(thesaurus)
'nan she nags i suspect' is the wordplay.
'suspect' indicates anagramming the letters.
'nan'+'she'+'nags'+'i'='nanshenagsi'
'nanshenagsi' anagrammed gives 'SHENANIGANS'.
'creating' is the link.
(Other definitions for shenanigans that I've seen before include "dirty work!" , "Monkey business" , "Mischievous trickery" , "Mischief; dishonest activity" .)