Administer punishment using 9-inch ruler? (5)
I believe the answer is:
spank
'administer punishment' is the definition.
'9-inch ruler?' is the wordplay.
'9-inch' becomes 'span' (unit of measurement roughly equal to 9 inches).
'ruler?' becomes 'k'.
'span'+'k'='SPANK'
'using' is the link.
(Other definitions for spank that I've seen before include "Beat" , "Slap; smack" , "chastise" .)