Heading off injury, first sign of danger and I'll pop into a ball (9)
I believe the answer is:
armadillo
'heading off injury first sign of danger and i'll pop into a ball' is the definition.
I can't judge whether this defines the answer.
'first sign of danger and i'll pop into a ball' is the wordplay.
'first sign of' says to take the initial letters.
'pop' indicates an anagram (I've seen 'popping' mean this (the original order pops or explodes)).
'into' is an insertion indicator.
'ball' becomes 'rmo' (I am not sure about this - if you are sure you should believe this answer much more).
The first letters of 'danger and' is 'da'.
'da'+'ill'='daill'
'daill' anagrammed gives 'adill'.
'a'+'rmo'='armo'
'adill' placed inside 'armo' is 'ARMADILLO'.
(Other definitions for armadillo that I've seen before include "Burrowing mammal with a covering of bony plates" , "Toothless Native American" , "Long-snouted animal" , "Bony-plated insectivore" , "Plated burrowing animal" .)