Actually when a substance is found before bad performance (2,1,6,2,4)
I believe the answer is:
as a matter of fact
'actually' is the definition.
(synonyms)
'when a substance is found before bad performance' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'a substance' becomes 'A' (A is an example).
'is found before' becomes 'matter' (I can't explain this - if you can you should believe this answer much more).
'bad' becomes 'off' (eg meat that's gone off is bad).
'performance' becomes 'act' (act is a kind of performance).
'as'+'a'+'matter'+'off'+'act'='AS A MATTER OF FACT'
Can you help me to learn more?
(Other definitions for as a matter of fact that I've seen before include "in reality" , "Actually" .)