Though fast, was beaten (6)
I believe the answer is:
lashed
'beaten' is the definition.
(lashing is a kind of beating)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for lashed that I've seen before include "Hit" , "Tied -- beaten" , "Verbally attacked" , "Tied; whipped" , "Flogged" .)