Charity event mostly to provide money for series of performances (3,3)
I believe the answer is:
fun run
'charity event' is the definition.
(I've seen this before)
'mostly to provide money for series of performances' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'to provide money for' becomes 'fund' (I've seen this before).
'series of performances' becomes 'run' (as in a theatrical run).
'fund' with its final letter removed is 'fun'.
'fun'+'run'='FUN RUN'
(Other definitions for fun run that I've seen before include "Race usually for charity" , "Charity sporting event" , "Unserious race" , "Footrace for enjoyment" , "Long distance race for amusement" .)