Two days before Ides of March, say, unluckily positioned? (10)
I believe the answer is:
thirteenth
I believe this clue is a double definition.
'two days before ides of march' is the first definition.
(the Ides of March is the fifteenth of March)
'unluckily positioned?' is the second definition.
(thirteen is supposedly unlucky)
'say' acts as a link.
(Other definitions for thirteenth that I've seen before include "Unlucky Friday?" , "interval" , "this would be so unlucky?" , "One later among these clues" , "Unlucky position in order" .)