In the centre, teenagers fight roughly (5)
I believe the answer is:
about
'roughly' is the definition.
(about can mean roughly or approximately)
'in the centre teenagers fight' is the wordplay.
'in the centre' means to look at the middle letters.
'fight' becomes 'bout' (as in a bout in boxing).
The middle letter of 'teenagers' is 'a'.
'a'+'bout'='ABOUT'
(Other definitions for about that I've seen before include "On the topic of" , "in action" , "Approximately, or in vicinity" , "Nearly" , "Concerning; roughly" .)