Jason's jacket in suit tailored for martial art (8)
I believe the answer is:
ninjitsu
'for martial art' is the definition.
(I've seen this before)
'jason's jacket in suit tailored' is the wordplay.
'jacket' says to hollow out the word (remove centre letters) (the letters worn by the word as a 'jacket' are use).
'tailored' indicates anagramming the letters (the letters are customised ).
'jason' with its middle taken out is 'jn'.
'jn'+'in'+'suit'='jninsuit'
'jninsuit' with letters rearranged gives 'NINJITSU'.
(Other definitions for ninjitsu that I've seen before include "Stealthy combat" , "martial art" .)