Prone to an outburst against rough calico around neck opening (8)
I believe the answer is:
volcanic
'prone to an outburst' is the definition.
(lava bursts out of a volcano)
'against rough calico around neck opening' is the wordplay.
'against' becomes 'v' (abbreviation for 'versus').
'rough' indicates an anagram (a rough or broken ordering of the letters).
'around' indicates putting letters inside.
'opening' indicates taking the first letters.
The first letter of 'neck' is 'n'.
'calico' with letters rearranged gives 'olcaic'.
'olcaic' going around 'n' is 'olcanic'.
'v'+'olcanic'='VOLCANIC'
(Other definitions for volcanic that I've seen before include "Like lava, perhaps" , "Of lava-producing fissures" , "Relating to mountains such as Vesuvius" , "given to sudden outbursts" , "Of Etna etc" .)