Show off, getting first of reds in pocket (4)
I believe the answer is:
brag
'show off' is the definition.
(I've seen this before)
'first of reds in pocket' is the wordplay.
'first of reds' becomes 'r' (1st letter of 'reds').
'in' indicates putting letters inside.
'pocket' becomes 'bag' (synonyms).
'r' put within 'bag' is 'BRAG'.
'getting' is the link.
(Other definitions for brag that I've seen before include "boast; form of poker" , "popular with 15 [EGOTIST] , no doubt" , "Shoot a line" , "Card game - boast" , "Blow one's own trumpet" .)