Overweight track racer faces defeat (7)

I believe the answer is:

trounce

I'm a little stuck... Click here to teach me more about this clue!

'defeat' is the definition.
(I know that trounce is a more specific form of defeat)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for trounce that I've seen before include "Defeat heavily (in contest)" , "Clobber" , "Beat soundly" , "Slaughter" , "Beat roundly" .)

I've seen this clue in The Daily Express.

Want a hint initially instead of a full solution? Install my app