Blackleg takes taxi after start of strike (4)
I believe the answer is:
scab
'blackleg' is the definition.
(synonyms)
'taxi after start of strike' is the wordplay.
'taxi' becomes 'cab' (synonyms).
'after' says to put letters next to each other.
'start of' indicates taking the first letters.
The first letter of 'strike' is 's'.
'cab' put 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" .)