Great and exciting performance influencing current leaders (4)
I believe the answer is:
epic
'great' is the definition.
'exciting performance influencing current leaders' is the wordplay.
'leaders' indicates taking the first letters.
The first letters of 'exciting performance influencing current' is 'EPIC'.
'and' acts as a link.
(Other definitions for epic that I've seen before include "Long account" , "A long poem or book with adventurous theme" , "Impressive scope" , "Vast in scale" , "Long poem telling of great events" .)