Become calm in court? (2,6)
I believe the answer is:
go steady
'court?' is the definition.
(to go steady with someone is to court or date them)
'become calm' is the wordplay.
'become' becomes 'go' (eg to go rotten is to become rotten).
'calm' becomes 'steady' (synonyms).
'go'+'steady'='GO STEADY'
'in' acts as a link.
(Other definitions for go steady that I've seen before include "Have relationship as regular boy or girl friend - sounds stable" , "Keep seeing each other" , "Court romantically" , "Date one person regularly" , "See someone regularly" .)