One's knotted, restricting oxygen! (5)
I believe the answer is:
noose
'one's knotted restricting oxygen' is the definition.
I can't judge whether this definition defines the answer.
'one's knotted restricting oxygen' is the wordplay.
'knotted' is an anagram indicator.
'restricting' means one lot of letters goes inside another.
'oxygen' becomes 'O' (O is the chemical symbol for oxygen).
'ones' with letters rearranged gives 'nose'.
'nose' enclosing 'o' is 'NOOSE'.
Can you help me to learn more?
(Other definitions for noose that I've seen before include "Catch" , "Hanging loop in rope" , "Bond" , "Loop formed by means of a slip knot" , "trap" .)