Justification in blocking prize money (5)
I believe the answer is:
point
'justification' is the definition.
'in blocking prize money' is the wordplay.
'blocking' means one lot of letters goes inside another.
'prize money' becomes 'pot'.
'in' put within 'pot' is 'POINT'.
(Other definitions for point that I've seen before include "Sharp or tapering end" , "See 10 Across" , "Indicate; promontory" , "Dot, punctuation mark" , "Geometric element that has position but no extension" .)