Second not out for the count? (4,2)
I believe the answer is:
back up
'second' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for back up that I've seen before include "Give support" , "Copy of a file on a separate storage device" , "Help & support - from behind?" , "provide support" , "Support, assist" .)