Out of practice, rugby guy's no amateur (5)
I believe the answer is:
rusty
'out of practice' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rusty that I've seen before include "affected by inactivity" , "Affected by corrosion - out of practice" , "(Of knowledge) not current" , "a bit faded" , "showing sign of inactivity?" .)