Brilliant strike, not straight (7)
I believe the answer is:
lambent
'brilliant' is the definition.
(something lambent is giving off some light)
'strike not straight' is the wordplay.
'strike' becomes 'lam' (to 'lam' means to hit hard).
'not straight' becomes 'bent' (crooked or bendy as opposed to straight).
'lam'+'bent'='LAMBENT'
(Other definitions for lambent that I've seen before include "Making stealthy moves" , "Flickering like malt, Ben" , "Brilliant and light of wit" , "Gleaming with a soft radiance, the moon perhaps" , "Of flame or light, playing about a surface" .)