Active agent safeguarding resistance (4)
I believe the answer is:
spry
'active' is the definition.
(similar in meaning)
'agent safeguarding resistance' is the wordplay.
I cannot really understand how this works, but
'resistance' could be 'r' (electronics abbreviation) and 'r' is located in the answer.
'agent' could be 'spy' (spy is a kind of agent) and 'spy' is found in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for spry that I've seen before include "'Agile, nimble (4)'" , "Light on one's feet" , "Energetic" , "Fleet" , "Alert" .)