Ominous batting, caught by sibling (8)
I believe the answer is:
sinister
'ominous' is the definition.
(synonyms)
'batting caught by sibling' is the wordplay.
'batting' becomes 'in' (as in batting or being 'in' in cricket).
'caught by' is an insertion indicator.
'sibling' becomes 'sister' (I've seen this before).
'in' inserted within 'sister' is 'SINISTER'.
(Other definitions for sinister that I've seen before include "Suggestive of evil, to the left in heraldry" , "Forbidding" , "not right!" , "Very unpleasant" , "Spooky" .)