Each to secure three points in addition (2,4)
I believe the answer is:
as well
'in addition' is the definition.
(I've seen this before)
'each to secure three points' is the wordplay.
'each' becomes 'all' (similar in meaning).
'to secure' is an insertion indicator (inserted letters are secured inside).
'three points' becomes 'SWE'.
'all' enclosing 'swe' is 'AS WELL'.
(Other definitions for as well that I've seen before include "on top" , "Also, additionally" , "with equal effect" , "A swell sort of addition" , "Appropriate" .)