Arguing in line in front of gymnasium (6)
I believe the answer is:
rowing
'arguing' is the definition.
(I've seen this before)
'line in front of gymnasium' is the wordplay.
'line' becomes 'row' (row is a kind of line**).
'front of' says to take the initial letters.
The first letter of 'gymnasium' is 'g'.
'row'+'in'+'g'='ROWING'
'in' acts as a link.
(Other definitions for rowing that I've seen before include "Olympic sport; arguing" , "in dispute" , "Sport associated with Henley" , "Propelling boat with oars" , "Steven Redgrave's sport" .)