Was emphatic that the side isn’t to be beaten (8)
I believe the answer is:
insisted
'was emphatic that' is the definition.
'insisted' can be an answer for 'was emphatic' (I've seen this before). I am not certain of the remainder of the definition.
'side isn't to be beaten' is the wordplay.
'to be beaten' is an anagram indicator (letters beaten up or destroyed).
'side'+'isnt'='sideisnt'
'sideisnt' anagrammed gives 'INSISTED'.
'the' is the link.
Can you help me to learn more?
(Other definitions for insisted that I've seen before include "Declared emphatically about tidiness" , "Stated positively and assertively" , "Declared or demanded emphatically" , "... repeated" , "Stated emphatically, refusing to budge" .)