Fights to get the breaks one's put in for (7)
I believe the answer is:
resists
'fights' is the definition.
(resisting is a kind of fighting)
'the breaks one's put in for' is the wordplay.
'the breaks' becomes 'rests' (rest is a kind of break).
'one's put' becomes 'si' (I can't explain this - if you can you should give a lot more credence to this answer).
'in for' indicates putting letters inside.
'rests' going around 'si' is 'RESISTS'.
'to get' acts as a link.
Can you help me to learn more?
(Other definitions for resists that I've seen before include "Opposes, puts up fight" , "Defends" , "Is reluctant" , "Sisters (anag.)" , "Defies" .)