Starts on the straight approach — right for leader (4)
I believe the answer is:
Here is my best explanation:
'leader' is the definition.
(I've seen this before)
'starts on the straight approach right' is the wordplay.
'starts on' says to take the initial letters.
The first letters of 'the straight approach right' is 'TSAR'.
'for' acts as a link.
(Other definitions for tsar that I've seen before include "Title given to the kings of Bulgaria", "Leader", "Monarch of old Russia", "Old Russian ruler", "autocrat", "Title of Russian emperor", "Autocrat", "Absolute ruler", "Rats (anag)" and "Word derived from Caesar, used by European rulers since 1547".)