Article's nothing without digital protection (4)
I believe the answer is:
nail
'digital protection' is the definition.
(a nail protects a digit)
'article's nothing without' is the wordplay.
'article' becomes 'a' (example of the part-of-speech).
'nothing' becomes 'nil' (eg nil is zero in football).
'without' means one lot of letters goes inside another.
'a' inserted within 'nil' is 'NAIL'.
(Other definitions for nail that I've seen before include "Fixer (on finger?)" , "it needs hammering home" , "SECOND PART OF 17" , "Hammered pin" , "Carpentry fastener" .)