Hold about fifty to share 50-50 (5)
I believe the answer is:
halve
'share 50-50' is the definition.
(I've seen this in another clue)
'hold about fifty' is the wordplay.
'hold' becomes 'have' (synonyms).
'about' means one lot of letters goes inside another.
'fifty' becomes 'L' (Roman numeral).
'have' placed around 'l' is 'HALVE'.
'to' is the link.
(Other definitions for halve that I've seen before include "Divide equally between two" , "make 10 5 say?" , "Divide into two equal parts" , "Split in two" , "cut by fifty percent" .)