Joy sends lag crazy (8)
I believe the answer is:
gladness
'joy' is the definition.
(I've seen this before)
'sends lag crazy' is the wordplay.
'crazy' indicates anagramming the letters.
'sends'+'lag'='sendslag'
'sendslag' with letters rearranged gives 'GLADNESS'.
(Other definitions for gladness that I've seen before include "Pleasure" , "Joy" , "Happy state" , "delight" .)