Introduction of full beam leads to quarrel (4)
I believe the answer is:
fray
'quarrel' is the definition.
(thesaurus)
'introduction of full beam' is the wordplay.
'introduction of' says to take the initial letters.
'beam' becomes 'ray' (synonyms).
The first letter of 'full' is 'f'.
'f'+'ray'='FRAY'
'leads to' acts as a link.
(Other definitions for fray that I've seen before include "discordant interchange" , "Ravel" , "Suffer peripheral damage" , "Unravel at an edge" , "Disturbance" .)