Diving position (4)
I believe the answer is:
pike
'diving position' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pike that I've seen before include "dive in this position" , "Fresh-water fish or old spear" , "Fish; weapon; hill" , "Fish and pole with a spearhead" , "may be hooked" .)