Lack of practice for play set in USSR (9)
I believe the answer is:
rustiness
'lack of practice' is the definition.
The definition suggests a singular noun which matches the answer.
'play set in ussr' is the wordplay.
'play' indicates an anagram.
'set'+'in'+'ussr'='setinussr'
'setinussr' is an anagram of 'RUSTINESS'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for rustiness that I've seen before include "being out of date?" , "Condition of being out of practice" , "Discolouration of age" .)