Start of appeal proceedings affecting particular chambers (6)
I believe the answer is:
atrial
'start of appeal proceedings affecting particular chambers' is the definition.
I can't judge whether this defines the answer.
'start of appeal proceedings' is the wordplay.
'start of' suggests taking the first letters.
'proceedings' becomes 'trial' (trial is a kind of proceedings).
The first letter of 'appeal' is 'a'.
'a'+'trial'='ATRIAL'
Can you help me to learn more?
(Other definitions for atrial that I've seen before include "Like some courts" , "of the heart cavities" , "Like main court" , "Lariat (anag)" , "referring to Chambers?" .)