Nothing in sumo wrestling is threatening (7)
I believe the answer is:
ominous
'is threatening' is the definition.
('ominous' can be a synonym of 'threatening')
'nothing in sumo wrestling' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'wrestling' indicates an anagram.
'in'+'sumo'='insumo'
'insumo' with letters rearranged gives 'minous'.
'o'+'minous'='OMINOUS'
(Other definitions for ominous that I've seen before include "Portending something bad" , "Threatening disaster" , "Threatening, looks bad" , "Forbidding" , "Boding badly, menacing" .)