Yours truly absorbing large, decisive blow (7)
I believe the answer is:
settler
'decisive blow' is the definition.
(I've seen this before)
'yours truly absorbing large' is the wordplay.
'yours truly' becomes 'setter' (the person who set this crossword).
'absorbing' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'setter' going around 'l' is 'SETTLER'.
(Other definitions for settler that I've seen before include "newcomer, perhaps" , "Coloniser - arbitrator" , "One taking up residence in a new area" , "Colonist, pioneer" , "Early colonist" .)