Happy marriage is a one-sided game? (4,5)
I believe the answer is:
love match
'happy marriage' is the definition.
'love match' can be an answer for 'marriage' (love match is a kind of marriage). I'm not sure about the 'happy' bit.
'one-sided game?' is the wordplay.
'one sided' becomes 'love' (I can't justify this - if you can you should give a lot more credence to this answer).
'game?' becomes 'match' (eg a football match).
'love'+'match'='LOVE-MATCH'
'is a' is the link.
Can you help me to learn more?
(Other definitions for love match that I've seen before include "This is not just a convenient arrangement" , "Marriage based on real affection" , "comes to nothing for one party [IN?] court?" , "romantic marriage" , "No score draw" .)