Senior I upset becomes more rowdy (7)
I believe the answer is:
noisier
'more rowdy' is the definition.
(I've seen this before)
'senior i upset' is the wordplay.
'upset' indicates anagramming the letters.
'senior'+'i'='seniori'
'seniori' anagrammed gives 'NOISIER'.
'becomes' acts as a link.
(Other definitions for noisier that I've seen before include "More rowdy" , "Perhaps more disturbing" , "Less quiet" , "More loud" , "Louder" .)