Blackleg takes taxi after start of strike (4)
I believe the answer is:
scab
'blackleg' is the definition.
(I know that blackleg can be written as scab)
'taxi after start of strike' is the wordplay.
'taxi' becomes 'cab' (synonyms).
'after' means one lot of letters go next to another.
'start of' indicates taking the first letters.
The first letter of 'strike' is 's'.
'cab' after 's' is 'SCAB'.
'takes' is the link.
(Other definitions for scab that I've seen before include "One continuing to work" , "one works during strike" , "sign of wound healing" , "Ignorer of strike" , "Blackleg - sign of injury" .)