Rope lassoing display of cowboy skill, mostly getting rusty (8)
I believe the answer is:
corroded
'rusty' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for corroded that I've seen before include "Eaten away chemically" , "like an old banger?" , "with holes in?" , "Rusted" .)