Declare, setting the target at 150 (5)
I believe the answer is:
claim
'declare' is the definition.
(I know that claim is a more specific form of the action affirm)
'the target at 150' is the wordplay.
'the target' becomes 'aim' (both can mean a goal or purpose).
'at' says to put letters next to each other (I've seen this in other clues).
'150' becomes 'CL' (Roman numerals).
'aim' put after 'cl' is 'CLAIM'.
'setting' acts as a link.
(Other definitions for claim that I've seen before include "State to be the case" , "Allegation" , "Right; demand this" , "Assertion of ownership etc" , "Cause the loss of (a life)" .)