Old bad actors overlooking a measure of resistance (4)
I believe the answer is:
ohms
'measure of resistance' is the definition.
(I've seen this before)
'old bad actors overlooking a' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'bad actors' becomes 'hams' (I've seen this in another clue).
'overlooking' suggests deleting specific letters.
'hams' with 'a' removed is 'hms'.
'o'+'hms'='OHMS'
(Other definitions for ohms that I've seen before include "Frank on official post" , "working for the monarchy?" , "degrees of resistance" , "Frank marking" , "measures of resistance" .)