Formidable bounce of seamer (8)
I believe the answer is:
fearsome
'formidable' is the definition.
(I've seen this before)
'bounce of seamer' is the wordplay.
'bounce' indicates anagramming the letters.
'of'+'seamer'='ofseamer'
'ofseamer' with letters rearranged gives 'FEARSOME'.
(Other definitions for fearsome that I've seen before include "Fame rose and became frightening" , "Terrifying" , "Frightening, terrible" , "Of frightening appearance" , "Formidable" .)