>>>Futbol - a gentlemen's game played by hooligans ;)
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>With hooligans in the bleachers as well.
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>It's happened in Rugby as well- e.g. at the 1924 Olympics, they put up a fence to protect the US players. In the 2015 World Cup the closest would be an enthusiastic fan joining in the recent South Africa-Samoa game. Periodically there are punch ups on the sidelines but that results in people being banned, possibly for life, and it's not expected that hooligans will turn up primed for trouble.
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>http://www.desertsun.co.uk/blog/?p=1917

I remember a few years back there was an unexpected experiment. There was a major football match with rabid fans from both sides but for some reason (police strike?) there was virtually no police presence, just a handful of "supervisor" types.

Despite that the game was played as scheduled, and to almost everyone's shock there were no serious incidents and practically no incidents of any kind.

I can't remember enough of the details to find a reference. At the time it was touted as support for the theory that if you have a ton of cops at a match, the fans will show up ready to fight. If there are no cops, they'll have to police themselves (or not). If things get really out of hand, they'd be on their own. Food for second thought.

This also holds true to some extent with protective equipment in contact sports. If rugby players start wearing helmets, there won't be any unspoken agreement to avoid hitting each other's heads.