7a Carriage left to deteriorate (7)
??R????
3d In defence, what is needed by the striker? (6)
????I?
12d For example, holding net finally run after butterfly (5)
S???R
1a Mixing pack, separating spades and diamonds? (10)
?C???????G
11d A key cleric backing bishop's fast, maybe? (6)
???E?B ADVERB?
13a Read out 'He, at heart will remain loyal' (6)
???E?E ADHERE?
6d Round by round, making a comeback in the ring (4)
???L BELL?
16a One way to fix a match, maybe (3)
??E TIE?
Yes, sorry, i can see adhere works. I went for cohere as a synonym of adher because I read the clue as starting at "He at heart..." and thought of HE and CORE