Pad, pre-set, tripped where boy racer nabbed? (5,4)
I believe the answer is:
speed trap
'where boy racer nabbed?' is the definition.
(a speed trap might catch a boy racer speeding)
'pad pre-set tripped' is the wordplay.
'tripped' indicates anagramming the letters (I've seen 'trip' mean this).
'pad'+'pre'+'set'='padpreset'
'padpreset' is an anagram of 'SPEED TRAP'.
(Other definitions for speed trap that I've seen before include "Police control" , "inconvenience for boy racers?" , "curse of drivers?" , "road safety measure" , "something drivers might avoid" .)