Fool about before preliminary round (5)
I believe the answer is:
cheat
'fool' is the definition.
(I've seen this in another clue)
'about before preliminary round' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'before' says to put letters next to each other.
'preliminary round' becomes 'heat' (I've seen this in another clue).
'c'+'heat'='CHEAT'
(Other definitions for cheat that I've seen before include "rook" , "Rogue" , "Take unfair advantage of" , "Teach? (Anag)" , "fleece" .)