Tenacious broadcaster buying Twitch (6)
I believe the answer is:
sticky
'tenacious' is the definition.
(tenacious can mean sticky or gluey)
'broadcaster buying twitch' is the wordplay.
'broadcaster' becomes 'sky' (Sky is a television company).
'buying' means one lot of letters goes inside another (inserted letters are acquired or 'bought').
'twitch' becomes 'tic' (tic is a kind of twitch).
'sky' going around 'tic' is 'STICKY'.
(Other definitions for sticky that I've seen before include "Difficult - adhesive" , "Awkward; tacky" , "Glutinous, gooey" , "Awkward - muggy" , "sultry?" .)