Sharp and tart? That's about right (5)
I believe the answer is:
acrid
'sharp' is the definition.
(I've seen this before)
'tart? that's about right' is the wordplay.
'tart?' becomes 'acid' (I've seen this before).
'that's about' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'acid' placed around 'r' is 'ACRID'.
'and' acts as a link.
(Other definitions for acrid that I've seen before include "Greek goddess" , "Sour, pungent" , "Stinging" , "Unpleasantly pungent" , "Bitterly pungent" .)