Deliberate tackle initially accepted by referee (8)
I believe the answer is:
meditate
'deliberate' is the definition.
(thesaurus)
'tackle initially accepted by referee' is the wordplay.
'initially' suggests taking the first letters.
'accepted by' is an insertion indicator.
'referee' becomes 'mediate' (I've seen this before).
The first letter of 'tackle' is 't'.
't' going within 'mediate' is 'MEDITATE'.
(Other definitions for meditate that I've seen before include "Engage in contemplation" , "Think contemplatively" , "Muse" , "Cogitate" , "Ruminate" .)