Dart off - your leader is overdue (5)
I believe the answer is:
tardy
'overdue' is the definition.
(I've seen this in another clue)
'dart off your leader' is the wordplay.
'off' indicates an anagram.
'leader' says to take the initial letters.
The initial letter of 'your' is 'y'.
'dart' with letters rearranged gives 'tard'.
'tard'+'y'='TARDY'
'is' acts as a link.
(Other definitions for tardy that I've seen before include "Backward" , "Late, delayed" , "Late; sluggish" , "Unpunctual" , "Behindhand" .)