Respond concerning performance (5)
I believe the answer is:
react
'respond' is the definition.
(to react to something is to respond to it)
'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 "Hit back" , "Take" , "Trace (anag)" , "Retaliate" , "Change chemically" .)