Beat the unending spots (6)
I believe the answer is:
thrash
'beat' is the definition.
(thrashing is a kind of beating)
'the unending spots' is the wordplay.
'unending' means to remove the last letter.
'spots' becomes 'rash' (I've seen this before).
'the' with its last letter taken away is 'th'.
'th'+'rash'='THRASH'
(Other definitions for thrash that I've seen before include "stuff" , "Drub" , "Administer severe beating to" , "Clobber" , "Noisy, lavish party" .)