Heartily congratulating rugby players getting a round ahead (12)
I believe the answer is:
backslapping
'heartily congratulating' is the definition.
I can't judge whether this defines the answer.
'rugby players getting a round ahead' is the wordplay.
'rugby players' becomes 'backs' (back is a type of rugby player).
'getting a round ahead' becomes 'lapping' (I can't explain this - if you can you should give a lot more credence to this answer).
'backs'+'lapping'='BACKSLAPPING'
Can you help me to learn more?
(Other definitions for backslapping that I've seen before include "Demonstratively cheery" , "Hearty" .)