Sinner and saint helping at protest (13)
I believe the answer is:
demonstration
'protest' is the definition.
(I know that protest can be written as Demonstration)
'sinner and saint helping' is the wordplay.
'sinner' becomes 'demon' (I can't explain this - if you can you should give a lot more credence to this answer).
'and' says to put letters next to each other.
'saint' becomes 'st' (abbreviation).
'helping' becomes 'ration' (a ration is a serving or helping).
'demon'+'st'+'ration'='DEMONSTRATION'
'at' acts as a link.
Can you help me to learn more?
(Other definitions for demonstration that I've seen before include "Exhibition, protest" , "March; proof" , "Display showing how something works" , "It's to voice protest" , "Protest meeting" .)