Showing ruddy obvious lack of practice (5)
I believe the answer is:
rusty
'practice' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for rusty that I've seen before include "Having a reddish-orange oxide coating" , "Antiquated" , "Oxidised, corroded" , "Behind the times" , "Impaired through lack of use" .)