Be caught within one mile: fool! (8)
I believe the answer is:
imbecile
'fool' is the definition.
(I've seen this before)
'be caught within one mile' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'within' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'be'+'c'='bec'
'i'+'mile'='imile'
'bec' placed inside 'imile' is 'IMBECILE'.
(Other definitions for imbecile that I've seen before include "A mentally deficient or stupid person" , "Numbskull" , "An unintelligent person, very low IQ" , "fool" , "Abusive word for foolish person" .)