A surprise or planned fight, when either (a)one individual is attacked/beaten by a group of 2 or more individuals or (b) when a notiably larger group attacks/fights a smaller group of individuals. These fights can occur with or without any kind of valid reason to jump someone.
A onesided fight.
verb jumped
"Man lets jump this kid coming this way on his bike"
"Me and my cousin are going to jump this guy that stole our car"
Underagers getting random strangers walking past to go into a shop and buy alcohol for them, literalluy jumping into the shop for them. Usually targeted are junkeys, alcoholics, students and foreigners.
OriginatedGlasgow/ any poor area with drink problems
Jason " How are we gonna get that booze for tonight"
Jonny " Theres a tramp over there. Come on lets get a jump in.