Lose enthusiasm for career in print, starting own family-sponsored company (3,3,2,5)
I believe the answer is:
run out of steam
'lose enthusiasm' is the definition.
(I've seen this before)
'career in print starting own family-sponsored company' is the wordplay.
'career' becomes 'run' (career can mean to run or move out of control).
'in print' becomes 'out' (as in a book that is out).
'starting' suggests taking the first letters.
'company' becomes 'team' (I've seen this before).
The first letters of 'own family sponsored' is 'ofs'.
'run'+'out'+'ofs'+'team'='RUN OUT OF STEAM'
'for' is the link.
(Other definitions for run out of steam that I've seen before include "Have no motive force left" , "Lose impetus" , "like Awdry's Thomas?" , "Lack the energy to continue" , "Lose enthusiasm" .)