Caught priests involved in illegitimate trade (7)
I believe the answer is:
trapped
'caught' is the definition.
(trapping is a kind of catching)
'priests involved in illegitimate trade' is the wordplay.
'priests' becomes 'PP' (two instances of an abbreviation for priest).
'involved in' means one lot of letters goes inside another.
'illegitimate' is an anagram indicator (a wrong or illegitimate spelling).
'trade' anagrammed gives 'traed'.
'pp' placed within 'traed' is 'TRAPPED'.
(Other definitions for trapped that I've seen before include "Snared" , "Stuck" , "in a tight corner" , "Caught" , "Ensnared, cornered" .)