Do not pierce carelessly! (9)
I believe the answer is:
reception
'do' is the definition.
(I've seen this before)
'not pierce carelessly' is the wordplay.
'carelessly' indicates anagramming the letters.
'not'+'pierce'='notpierce'
'notpierce' is an anagram of 'RECEPTION'.
(Other definitions for reception that I've seen before include "Formal function" , "drinks party" , "First class" , "Entrance for office" , "signal quality" .)