Sports can be brutal both on the field, or in the pool, and off. Nationalistic resentments are often reflected in the matches and in the stands. But ultimately, isn't it just about winning?
Water polo players from Germany and Romania fight for the ball during a match in Debrecen, Hungary, in 2007.
Water polo is brutally physical. It's constant swimming but there's also a violent side. As a viewer, it's almost invisible. To the players, what's happening out of sight is a nasty mix of judo and karate.
"Under the water, everything is allowed," says Živko Gocić, captain of Serbia's national water polo team. "I don't want to say we are killing each other but physically it's a very tough sport and it's very rough."
The intensity of the matches under the water is often matched by the intensity of nationalist feeling in the stands, where, among those watching, things can get violent.
But Croatian and Serbian water polo matches are not the only ones that spark a rivalry that can then turn into nationalistic fervor. From European and World Cup soccer matches to the Olympic Games, support, or even opposition, of a particular team promotes strong feelings of patriotism.
"[Nationalism] is a highly prominent feature of the sporting world," says sociologist Alan Bairner, who has researched the connection between nationalism and sports. "Most major competitions are based around ideas of national teams supported by fans who want to celebrate their nationhood and the games are preceded by playing the national anthems."
Political tensions, sporting violence
When Gocić, growing up in what was then Yugoslavia first started playing water polo, he was just six years old, growing up in what was then Yugoslavia. Even then sporting events between Croatian and Serbian teams had a history of violence. As tensions grew between the two ethnic groups in the late 80s, anger and violence spilled over into soccer.
In 1990, two teams - one Serbian and one Croatian - played a Yugoslavian league match that turned into a full-fledged riot. One Croatian player was photographed kicking a policeman in a moment that some have cited as the start of the Croatian war of independence.
But Bairner is skeptical that the game kicked off the conflict. He says it is often more a case that sports reflect the political situation, rather than being the cause. "It's pretty clear that for Croatia and Serbia, there were significant tensions in that part of the world before the famous game in 1990. Tensions have to exist in the first place."
Those tensions have persisted over the years despite the breakup of Yugoslavia. While Croatia and Serbia are now separate states political problems between the two countries has still led to violence at a number of sporting events.
When Gocić was just starting out on Serbia's national team in 2003, a riot marred the final of the European Water Polo Championship. When Serbia won in overtime against Croatia, the Serbian foreign minister celebrated by jumping into the pool. Croatian fans rioted, burning the Serbian flag. It was eight years after the end of the Yugoslav Wars and the crowds watching the sport were charged with nationalist fury.
"For us, playing Croatia is not always just a sport," says Gocić. "There are things from history."
A matter of history
Historic conflicts and rivalries have often in the past been a catalyst for violence in the sporting scene. In his 1945 essay, The Sporting Spirit, writer George Orwell argues that international sports is "mimic warfare."
In 1969, a series of riots during the qualifying matches for the 1970 Soccer World Cup turned into a conflict between El Salvador and Honduras that became known as the "football war." In both cricket and football matches, crowds with a nationalist bent have turned on each other in Sri Lanka, Iran and Egypt.
But it is not only between countries that sporting events can become hostile. Bairner studied the role of sports in a divided Northern Ireland, where there were tensions between the largely Protestant unionists and the largely Catholic republicans.
"Football was a game played by both Catholics and Protestants and so became a flashpoint," he says, adding that: "Tensions in sporting contests may not be helpful but it doesn't mean they make things worse if they are bad already."
In Bairner's home Scotland, there have also been rivalries particularly with the England football team. And more than Scotland just winning - if the Scotland team does not make it through an international contest, England should still be beaten.
But as to whether it leads to significant problems all comes down to context, he says. "Very often it is cathartic; a safety valve. If terrible things are sung at football games, people then go home and behave in a respectable manner. In the UK, it's part of maintaining sport identities, mostly it can be kept under control."
Sport: bringing people together
Still, sport is also used to bring nations, and humanity as a whole, together. The International Olympic Committee's Olympic charter cites the fundamental principles of Olympism as using sports to promote harmonious relationships within humanity and creating a peaceful society.
Bairner has reservations. "I think a lot of sport for peace projects only manage to access people who aren't really a problem… my problem is that sport is too competitive."
Hope for peace
In January 2016, the European Water Polo Championship will be hosted in Serbia's capital, Belgrade. As the contest approaches, Gocić is of two minds: He is filled with nationalist pride and looking to perform well for his country. He also wants to play down any nationalistic tensions.
"We are just sportsmen," says Gocić. "We are just trying to represent our countries in the best way. When I am in the water, I don't think about my opponent - where he's from, his name - I am just concentrating on what we have to do in the water."
Ultimately, says Gocić, when you're involved in a match, it is less about nationalistic rivalry. You are simply playing to win. "What happened 20 years ago, it's passed," says Gocić. "We just have to move on. We are living in the present."