Opposed directly, one had adapted (4-2)
I believe the answer is:
head-on
'opposed directly' is the definition.
(as in a head-on collision)
'one had adapted' is the wordplay.
'adapted' indicates anagramming the letters.
'one'+'had'='onehad'
'onehad' with letters rearranged gives 'HEAD-ON'.
(Other definitions for head-on that I've seen before include "One had (anag.)" , "Of car crash, full frontal" , "This collision is full frontal" , "Collision happening in full-frontal way" , "(Of crash) involving the front of vehicle)" .)