A bird goes crazy without oxygen (5)
I believe the answer is:
goose
'a bird' is the definition.
(goose is a kind of bird)
'goes crazy without oxygen' is the wordplay.
'crazy' is an anagram indicator.
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'oxygen' becomes 'O' (atomic symbol for oxygen).
'goes' with letters rearranged gives 'gose'.
'gose' placed around 'o' is 'GOOSE'.
(Other definitions for goose that I've seen before include "Christmas bird?" , "Grab seat" , "Web-footed long-necked bird" , "Large water bird" , "Marches in an odd fashion" .)