It appears that even those lawless rebels who insist on running onto the field have a code, and the number one rule is: Don't run onto an opposing team's field. A Slovakian fan of MFK Kosice found this out the hard way when he took the field following a win at Slovan Bratislava.
In the above video you see the MFK fan reveling in a victory on the pitch, when another fan comes out of the stands and knocks him out with a haymaker to the throat.
For some reason, none of this is compelling enough to stadium staff or security for them to break out of a light jog, and the home fan is able to escape back into the stands as the riot squad halfheartedly attempts to beat him with their police clubs. [Lookit]