Professional players finally slaughtered (7)
I believe the answer is:
skilled
'professional' is the definition.
(similar in meaning)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for skilled that I've seen before include "Adept, clever" , "Competent - experienced" , "Talented" , "Expert, adroit" , "Showing great aptitude" .)