Against pieces of evidence? No point - I have to be convincing (10)
I believe the answer is:
conclusive
'convincing' is the definition.
(I've seen this before)
'against pieces of evidence? no point i have' is the wordplay.
'against' becomes 'con' (as in pros and cons, for and against).
'pieces of evidence? no' becomes 'clu' (I can't justify this - if you can you should give a lot more credence to this answer).
'point' becomes 's' (South).
'i have' becomes 'I've' (contraction of 'I have').
'con'+'clu'+'s'+'ive'='CONCLUSIVE'
'to be' is the link.
Can you help me to learn more?
(Other definitions for conclusive that I've seen before include "Final" , "Decisive, convincing" .)