Batting streak, it's said, having no effect (2,4)
I believe the answer is:
in vain
'having no effect' is the definition.
I can't judge whether this definition defines the answer.
'batting streak it's said' is the wordplay.
'batting' becomes 'in' (as in batting or being 'in' in cricket).
'streak' becomes 'vein' (vein can mean a streak or strip).
'it's said' indicates a 'sounds like' (homophone) clue.
'vein' is a homophone of 'vain'.
'in'+'vain'='IN VAIN'
Can you help me to learn more?
(Other definitions for in vain that I've seen before include "useless" , "To no end" , "Futile" , "Uselessly, without result" , "Unsuccessfully" .)