Subdued when there aren't many exciting openings (4)
I believe the answer is:
tame
'subdued' is the definition.
(similar in meaning)
'there aren't many exciting openings' is the wordplay.
'openings' indicates taking the first letters (I've seen 'opening of' mean this).
The first letters of 'there arent many exciting' is 'TAME'.
'when' is the link.
(Other definitions for tame that I've seen before include "Flat" , "Broken in" , "Domisticated with meat" , "Not exciting; domesticate" , "Domesticated kind of meat" .)