Out of practice, dependable opener's dismissed (5)
I believe the answer is:
rusty
'out of practice' is the definition.
(synonyms)
'dependable opener's dismissed' is the wordplay.
I cannot really see how this works, but
'dismissed' could be 'st' and 'st' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for rusty that I've seen before include "showing sign of inactivity?" , "Reddish," , "affected by inactivity" , "Oxidised, corroded" , "Having a reddish-orange oxide coating" .)