Measures introduced by Hampshire (4)
I believe the answer is:
amps
'measures' is the definition.
(amp is a kind of measure)
'introduced by hampshire' is the wordplay.
'introduced by' indicates a hidden word.
'AMPS' can be found hidden inside 'hampshire'.
(Other definitions for amps that I've seen before include "Current measures" , "Spam (anag)" , "concert gear" , "'Units of electric current, in short (4)'" , "Units of electrical power" .)