Initially sent inside, taunts without warrant (8)
I believe the answer is:
needless
'without warrant' is the definition.
('warrant' can be 'need' (thesaurus) so maybe 'without warrant' can be ''needless')
'initially sent inside taunts' is the wordplay.
'initially' indicates taking the first letters.
'inside' is an insertion indicator.
'taunts' becomes 'needles' (needle can mean to taunt or annoy).
The first letter of 'sent' is 's'.
's' going inside 'needles' is 'NEEDLESS'.
(Other definitions for needless that I've seen before include "Unnecessary and unwarranted" , "Superfluous" , "Gratuitous" , "Excessive" , "without provocation?" .)