Answer concerning performance (5)
I believe the answer is:
react
'answer' is the definition.
(I know that answer is a more specific form of the action react)
'concerning performance' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'performance' becomes 'act' (act is a kind of performance).
're'+'act'='REACT'
(Other definitions for react that I've seen before include "Act as opponent" , "Change chemically" , "Respond to a stimulus" , "What a chemical might do" , "Acknowledge" .)