Lace into rat involved in quarrel (11)
I believe the answer is:
altercation
'quarrel' is the definition.
(altercation is a kind of quarrel)
'lace into rat involved' is the wordplay.
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'lace'+'into'+'rat'='laceintorat'
'laceintorat' is an anagram of 'ALTERCATION'.
'in' acts as a link.
(Other definitions for altercation that I've seen before include "heated argument" , "Rattle a coin (anag) - row" , "Spat" , "Squabble" , "heated dispute" .)