Shun support and leave Six Nations team short on energy (2,2,5)
I believe the answer is:
go it alone
'shun support' is the definition.
I know nothing about this answer so I can't judge whether this works.
'leave six nations team short on energy' is the wordplay.
I cannot really understand how this works, but
'leave' could be 'go' (to go is to depart or leave) and 'go' is found within the answer.
'on' is found in the answer.
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is present in the answer.
The remaining letters 'ital' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'and' acts as a link.
Can you help me to learn more?
(Other definitions for go it alone that I've seen before include "Take something on on one's own" , "set up as freelancer" , "act without help" , "Proceed without the help of others" , "Act on one's own" .)