Be holding a tar baby (4)
I believe the answer is:
babe
'baby' is the definition.
('babe' can be a synonym of 'baby')
'be holding a tar' is the wordplay.
'holding' means one lot of letters goes inside another.
'a tar' becomes 'ab' (**).
'be' going around 'ab' is 'BABE'.
(Other definitions for babe that I've seen before include "One of the little people" , "Ruth, say" , "one up in arms" , "Ruth possibly" , "- Ruth, famous US baseball player" .)