Old Chinese leader grabbing tail of black shark (4)
I believe the answer is:
mako
'shark' is the definition.
(I know that mako is a type of mackerel shark)
'old chinese leader grabbing tail of black' is the wordplay.
'old chinese leader' becomes 'Mao' (Chairman Mao).
'grabbing' means one lot of letters goes inside another.
'tail of' indicates one should take the final letters.
The last letter of 'black' is 'k'.
'mao' going around 'k' is 'MAKO'.
(Other definitions for mako that I've seen before include "Shark" , "NZ tree" .)