Constantly breaking Nancy's tiles (11)
I believe the answer is:
incessantly
'constantly' is the definition.
(thesaurus)
'breaking nancy's tiles' is the wordplay.
'breaking' is an anagram indicator.
'nancys'+'tiles'='nancystiles'
'nancystiles' is an anagram of 'INCESSANTLY'.
(Other definitions for incessantly that I've seen before include "Continually" , "All the time" , "Never-endingly" .)