Scorpion? A sudden sally will protect chief, note (8)
I believe the answer is:
arachnid
'scorpion?' is the definition.
(scorpion is a kind of arachnid)
'a sudden sally will protect chief note' is the wordplay.
'sudden sally' becomes 'raid' (I've seen this in another clue).
'will protect' indicates putting letters inside (inserted letters are held or protected).
'chief' becomes 'ch' (abbreviation).
'note' becomes 'n' (abbreviation).
'ch'+'n'='chn'
'raid' going around 'chn' is 'rachnid'.
'a'+'rachnid'='ARACHNID'
(Other definitions for arachnid that I've seen before include "Class of animals including spiders and scorpions" , "One of species including spiders, scorpions etc" , "tick for one" , "Spider, mite, tick etc.; had in car (anag.)" , "Spider in a chard" .)