Introvert, individual splitting left and right (5)
I believe the answer is:
loner
'introvert' is the definition.
(I've seen this in another clue)
'individual splitting left and right' is the wordplay.
'individual' becomes 'one' (an individual is one person).
'splitting' means one lot of letters goes inside another (some letters split a word into two).
'left and right' becomes 'LR' (abbreviations for left and right).
'one' inserted inside 'lr' is 'LONER'.
(Other definitions for loner that I've seen before include "Person shunning company" , "No mixer" , "One who avoids company" , "One shunning society" , "One shunning company" .)