Unhappy about having lead in sprint (4)
I believe the answer is:
dash
'sprint' is the definition.
(I know that sprint can be written as dash)
'unhappy about having lead' is the wordplay.
'unhappy' becomes 'sad' (associated in meaning).
'about' is a reversal indicator.
'lead' indicates taking the first letters.
The first letter of 'having' is 'h'.
'sad' backwards is 'das'.
'das'+'h'='DASH'
'in' is the link.
(Other definitions for dash that I've seen before include "Run quickly - little taste - hyphen" , "scotch" , "style" , "gratuity" , "Hyphen - bother!" .)