Deliberate tackle's first caught by referee (8)
I believe the answer is:
meditate
'deliberate' is the definition.
(thesaurus)
'tackle's first caught by referee' is the wordplay.
'first' indicates taking the first letters.
'caught by' is an insertion indicator.
'referee' becomes 'mediate' (I've seen this before).
The first letter of 'tackles' is 't'.
't' put into 'mediate' is 'MEDITATE'.
(Other definitions for meditate that I've seen before include "Ponder" , "Consider thoughtfully" , "Think intently and at length" , "Relax mentally" , "Reflect upon" .)