Readers less rash possibly in- the performance dry runs (5,10)
I believe the answer is:
dress rehearsals
'dry runs' is the definition.
(dress rehearsal is a kind of dry run)
'readers less rash possibly' is the wordplay.
'possibly' is an anagram indicator.
'readers'+'less'+'rash'='readerslessrash'
'readerslessrash' is an anagram of 'DRESS REHEARSALS'.
'in-the performance' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Another definition for dress rehearsals that I've seen is " full-scale practices".)