Idiots beginning to startle judge (6)
I believe the answer is:
assess
'judge' is the definition.
(assessing is a kind of judging)
'idiots beginning to startle' is the wordplay.
'idiots' becomes 'asses' (I've seen this before).
'beginning to' indicates taking the first letters.
The initial letter of 'startle' is 's'.
'asses'+'s'='ASSESS'
(Other definitions for assess that I've seen before include "Estimate, gauge" , "Test" , "Fix the amount of tax" , "Rate, evaluate" , "Judge the quality of" .)