Psych out every second resident of Perth? (4)
I believe the answer is:
scot
'resident of perth?' is the definition.
(I've seen this in another clue)
'psych out every second' is the wordplay.
'every second' means one should take alternating letters (I've seen 'every second of' mean this).
'psych'+'out'='psychout'
The alternate letters of 'psychout' are 'SCOT'.
(Other definitions for scot that I've seen before include "Someone from north of the border?" , "Native of northern Great Britain" , "A Caledonian?" , "Eg, a Glaswegian" , "Native of Caledonia" .)