Formal sporting rules? (5,4)
I believe the answer is:
dress code
'formal sporting rules?' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'formal sporting rules?' is the wordplay.
'formal' becomes 'dress' (similar in meaning).
'sporting rules?' becomes 'code' (I am not sure about the 'sporting' bit.).
'dress'+'code'='DRESS CODE'
Can you help me to learn more?
(Other definitions for dress code that I've seen before include "Guidelines" , "Convention governing clothes to be warn on a particular occasion" , "Expected standard of attire" , "Stipulated attire" .)