Worker supporting first man to get tough (7)
'tough' is the definition.
'worker supporting first man' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'first man' becomes 'adam' (I've seen this before).
'ant' put after 'adam' is 'ADAMANT'.
'to get' acts as a link.
(Other definitions for adamant that I've seen before include "Resolute, refusing to yield", "Positive and unrelenting", "Inflexible, obdurate", "Firmly unchanging", "intractable".)