Guardian maybe supporting cricket side in theory (2,5)
I believe the answer is:
on paper
'in theory' is the definition.
(synonyms)
'guardian maybe supporting cricket side' is the wordplay.
'guardian maybe' becomes 'paper' (the Guardian is a newspaper).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'cricket side' becomes 'on' (cricket term, on or leg side).
'paper' after 'on' is 'ON PAPER'.
(Other definitions for on paper that I've seen before include "Planned (in theory)" , "As written - in theory" , "Hypothetically" , "Propane (anag.)" , "Theoretically" .)