Defence group expected to be excessive (5)
I believe the answer is:
undue
'be excessive' is the definition.
(synonyms)
'defence group expected' is the wordplay.
'defence group' becomes 'un' (I can't explain this - if you can you should believe this answer much more).
'expected' becomes 'due' (similar in meaning).
'un'+'due'='UNDUE'
'to' is the link.
Can you help me to learn more?
(Other definitions for undue that I've seen before include "Extreme" , "Excessively, unreasonably" , "Inappropriate - excessive" , "Excessive, unreasonable" , "Not warranted" .)