Intercept leader of force (4,3)
I believe the answer is:
head off
'intercept' is the definition.
(I've seen this before)
'leader of force' is the wordplay.
'leader' becomes 'head' (head is a kind of leader**).
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'head'+'of'+'f'='HEAD OFF'
(Other definitions for head off that I've seen before include "Block" , "Deflect from a path" , "Avoid" , "Stop" , "Deflect (decapitated?)" .)