Knocked for six in defeat (8)
I believe the answer is:
overcome
'defeat' is the definition.
(I know that overcome is a more specific form of beat)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for overcome that I've seen before include "Speechless" , "'Engulfed, by emotion say (8)'" , "Emotionally affected" , "hammer" , "Overwhelm (someone)" .)