Ditch, the largest, is jumped initially the wrong way (4)
I believe the answer is:
jilt
'ditch' is the definition.
(I've seen this before)
'the largest is jumped initially the wrong way' is the wordplay.
'initially' indicates taking the first letters.
'the wrong way' says the letters should be written in reverse.
The initial letters of 'the largest is jumped' is 'tlij'.
'tlij' backwards is 'JILT'.
(Other definitions for jilt that I've seen before include "Abandon at the altar" , "Discard abruptly" , "Abruptly reject lover" , "Cast aside capriciously" , "Ditch" .)