Boxer perhaps less heavy after change of starter (7)

I believe the answer is:

fighter

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'boxer perhaps' is the definition.
(I know that boxer is a type of martial artist)

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for fighter that I've seen before include "Boxer; warrior" , "Freight (anag.)" , "Plane" , "Combat aircraft" , "Combatant, battler" .)

I've seen this clue in The Telegraph.

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