Legal lead-in (4)
I believe the answer is:
para
'legal lead-in' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for para that I've seen before include "Soldier who jumps to order? (abbr)" , "abbreviated passage having unity" , "Soldier that jumps from planes" , "Soldier who's dropped in? (abbr)" , "Air-drop soldier" .)