Blood experts attempt to restrict nitrogen (8)
I believe the answer is:
ancestry
'blood' is the definition.
(I know that blood can be written as ancestry)
'experts attempt to restrict nitrogen' is the wordplay.
'experts' becomes 'aces' (ace is a kind of expert).
'attempt to' becomes 'try' (I've seen this in other clues).
'restrict' is an insertion indicator.
'nitrogen' becomes 'N' (N is the chemical symbol for nitrogen).
'aces'+'try'='acestry'
'acestry' placed around 'n' is 'ANCESTRY'.
(Other definitions for ancestry that I've seen before include "Line of forebears" , "race" , "Any crest (anag.)" , "Person's ethnic descent" , "Lineage" .)