Fought trade unions over first of strikes ahead (7)
I believe the answer is:
tussled
'fought' is the definition.
(tussling is a kind of fighting)
'trade unions over first of strikes ahead' is the wordplay.
'trade unions' becomes 'TUs' (abbreviation).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'first of strikes' becomes 's' (1st letter of 'strikes').
'ahead' becomes 'led' (to lead is to go ahead).
'tus'+'s'+'led'='TUSSLED'
(Other definitions for tussled that I've seen before include "Struggled in a confused way" , "was struggling" , "Fought" .)