On paper the irony's wasted (2,6)
I believe the answer is:
in theory
'on paper' is the definition.
('in theory' can be a synonym of 'on paper')
'the irony's wasted' is the wordplay.
'wasted' indicates anagramming the letters.
'the'+'irony'='theirony'
'theirony' is an anagram of 'IN THEORY'.
(Other definitions for in theory that I've seen before include "according to the assumed facts" , "On paper" , "In principal" , "Ideally" .)