Cheer from unruly yahoo outside front of restaurant (6)
I believe the answer is:
hooray
'cheer' is the definition.
(I've seen this before)
'unruly yahoo outside front of restaurant' is the wordplay.
'unruly' indicates an anagram.
'outside' is an insertion indicator.
'front of' says to take the initial letters.
The first letter of 'restaurant' is 'r'.
'yahoo' is an anagram of 'hooay'.
'hooay' enclosing 'r' is 'HOORAY'.
'from' is the link.
(Other definitions for hooray that I've seen before include "Joyous exclamation" , "Yippee!" , "Shout of approval" , "Hurrah" , "Exclamation of joy or victory" .)