Brilliant strike by criminal (7)
I believe the answer is:
lambent
'brilliant' is the definition.
(thesaurus)
'strike by criminal' is the wordplay.
'strike' becomes 'lam' (to 'lam' means to hit hard).
'by' is a charade indicator (letters next to each other).
'criminal' becomes 'bent' (I've seen this before).
'lam'+'bent'='LAMBENT'
(Other definitions for lambent that I've seen before include "inflamed?" , "Glowing with a soft radiance" , "Of flame or light, playing about a surface" , "Making stealthy moves" , "Softly bright or radiant; flickering" .)