New anorak covering good old jumper (8)
I believe the answer is:
kangaroo
'jumper' is the definition.
(animal which jumps)
'new anorak covering good old' is the wordplay.
'new' is an anagram indicator.
'covering' means one lot of letters goes inside another.
'good' becomes 'g' (abbreviation).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'anorak' is an anagram of 'kanaro'.
'kanaro' going around 'g' is 'kangaro'.
'kangaro'+'o'='KANGAROO'
(Other definitions for kangaroo that I've seen before include "Hopping marsupial" , "Jumping marsupial" , "Marsupial that boxes" , "Large Australian mammal" , "Antipodean marsupial" .)