Even if you're tens of thousands of miles away from the site of a rivalry match in the world of competitive football, the intensity of the visuals and sounds on television - black smoke wafting like ghastly apparitions, road flares being winged onto the pitch, all of which mixed with the Gregorian-style chants from supporters - it has the effect of transporting a person inside a world where people are willing to die for their love of club and country.
If you needed further proof as to the fervor for which people feel for their football allegiances, the European Championship solidified that notion after bouts of hooliganism threatened the earliest days of the tournament after English, Russian, and Croatian fans took to the streets and stands to run amok and were warned by FIFA that their exploits might result in their team's expulsion.
While national teams often evoke patriotic feelings, club level rivalries - specifically of the derby sorts where teams share the same city - are often the most dangerous and violent despite sharing neighborhoods and working alongside people who are ultimately viewed as enemies.
While most think of El Clásico between Barcelona FC and Real Madrid - or more local derbies like Aresnal vs. Spurs as proof of heated rivalries on the pitch - there are several lesser-known instances which are the most dangerous for fans and players alike.
West Ham United vs. Millwall F.C.
Name: Dockers Derby Where: London, England
The rivalry between West Ham and Millwall gets its name from the late 1800s when Thames Ironworks and Millwall Athletic drew support from local dockworkers at shipyards on either side of the River Thames who were vying for the same contracts and ultimately ended up hating each other after the Millwall shipyard broke a 1926 dockers' strike.
Trouble between the two sides is often attributed to the firms that support the clubs; the Inter City Firm and the Millwall Bushwackers, respectively - the latter of which has been known to use a "Millwall brick" - an improvised weapon composed of tightly manipulated newspaper that can be used as a shillelagh or a waddy and which can stealthily be slipped inside stadiums with even the tightest security.
Although there has been over a century of bloodshed, several events beginning in the 1970s proved to lay the foundation for the contemporary violence.
In 1972, a testimonial match took place between the sides to honor Harry Cripps who had played for both teams. This was marred by fighting both in and outside of the stadium.
Four years later, a Millwall fan, Ian Pratt, died in a skirmish with West Ham fans at New Cross station that led to his fall under a train.
According to The Telegraph, "Leaflets were later handed out in the Den's Cold Blow Lane end with a grainy picture of Pratt and a declaration in capital letters: 'A West Ham fan must die next week to avenge him.'"
The rivalry was only further intensified when Millwall earned a promotion to the First Division in 1988. While it would be the only season both would play with the same things at stake on the highest level, it proved to only make the hatred that much deeper.
In 2006, while England played host to Paraguay in their World Cup opener in Frankfurt, 16 were hurt after 100 rival West Ham and Millwall supporters fought each other in Canada Square, London's DOCKLANDS.
The most recent high-profile clash between the clubs occurred in 2009 as part of a second round match for the Football League Cup at West Ham's Boleyn Ground, in Upton Park, where 20 people were injured/stabbed.
West Ham and Millwall have only played twice since the Upton Park riot.
FC Red Star vs. Partizan
Name: The Eternal Derby Where: Belgrade, Serbia
The Serbian capital's two biggest clubs, Red Star and Partizan, are notoriously violent even in a football context.
Dating back to 1945, each club was formed in response to the events of post World War II communist Yugoslavia - with Red Star backed by the "United alliance of anti-fascist Youth," a communist organization - while Partizan was founded as the sports association of the Yugoslav People's Army and favored by then President, Josip Broz Tito, a Croat, who ruled Yugoslavia until his death in 1980.
With Red Star ultras dubbed "Delije" and Partizan fans called “Grobari” (Undertakers), their hatred stems from the complicated breakup of the former Yugoslavia which saw horrific instances of ethnic cleansing which resulted in 100,000 people dead by 1995 - the worst act of genocide since the Nazi regime’s destruction of some six million European Jews during World War II.
As VICE noted, "Red Star and Partizan remain major centers of Serbian ethnic nationalism—the same sentiment that led to civil war and ethnic cleansing in the region in the 1990s."
Although complicated in nature, Red Star has ties to one of Serbia's most infamous paramilitary groups, the Serbian Volunteer Guard, or Arkan's Tigers, was founded by a group of Red Star Belgrade fans in 1990 and led by Željko Ražnatović, known as Arkan, who was a wanted criminal by Interpol.
"I have watched football in 70 countries and written a book on derbies around the world but never have I seen so many police around one game," ESPN FC writer, Andy Mitten, noted.
The rivalry turned deadly in 1999 when 17-year-old Aleksandar Radovic was killed in Partizan Stadium after he was struck by a flare.
Two years ago, 104 arrests were made, with Red Star supporters burning seats at full-time.
Finally, last April's match was halted 45 minutes after police were pelted by missiles and flares.
Fenerbahce vs. Galatasaray
Name: Intercontinental Derby/Eternal Rivarly Where: Istanbul, Turkey
Dating back to 1909, the Istanbul-based derby between two of Turkey's biggest powerhouses in the Süper Lig, Fenerbahce and Galatasaray, really became the hotly-contested rivalry we know today when a friendly turned violent between both fans and players alike in 1934.
Unlike traditional derbies in which teams are separated by only a few miles, Fenerbahce and Galatasaray are divided by the Bosphorus straits and are on different continents (Fenerbahce in Asia and Galatasaray in Europe).
Fenerbahce is considered the more "working class" club in Istanbul and was formed in secret due to strict Ottoman rule in which the Sultan Abdul Hamid II forbade the Turkish youth to play football, while Galatasaray has enjoyed more success on the pitch - most notably winning the 2000 UEFA Cup against Arsenal - where it became the first Turkish side to win the contest and a European honor.
The 2012 derby between the clubs ended with police protecting Galatasaray players with riot shields, and with a Galatasaray supporter stabbed in the street.
In May 2013, 20-year-old Burak Yildirim, a Fenerbahce fan, was stabbed by two Galatasaray fans on his way home following the clash between the two clubs.
Despite the tensions, both clubs actually came together that same year in protest over the redevelopment of Istanbul's historic Taksim Square as well as Prime Minister Tayyip Erdogan's government.
"We are normally enemies, but this has really brought us together. It's never happened before," Mert Gurses, 18, told Reuters.
In May of this year, the annual derby was abruptly called off two hours before match was scheduled to take place, with police reasoning "the assessment of serious intelligence" as it related to unspecified threats.
KS Cracovia vs. Wisla Krakow
Name: The Holy War Where: Krakow, Poland
The city of Krakow has earned the unfortunate nickname of "The City of Knives" due to the exploits of football ultras who usually consider themselves fans of either KS Cracovia or Wisla Krakow and speaks to their refusal to sign the “Poznan agreement” which was established by officials so that firms wouldn't use weapons during their entanglements.
The first fully documented Krakow derby took place on September 20, 1908 in the Blonia area, where both clubs’ stadiums are now located.
Like other rivalries, the hatred between both groups stems from political leanings as well as religious undertones.
Wisla Krakow, also called Biala Gwiazda (White Star) was once owned by the communist police.
KS Cracovia, or Pasy (Stripes), is believed to have supposed Jewish roots. In turn, supporters have embraced the anti-Semitic rhetoric by Wisla and refers to their supporters as the "Jude Gang."
Even the events of World War II could hardly dampen the hatred between KS Cracovia and Wisla Krakow despite Adolf Hitler's ban of all sports in occupied Poland. Undeterred, illegal games were played on a regular basis - resulting in a notable instance of violence in 1943 where players and fans duked it out in the Ludwinow district in the city.
Just 10 days after Poland's liberation, Cracovia and Wisla squared off with incomplete squads and a referee who was decidedly a Wisla supporter.
In September 2003, a 23-year-old man was accosted by a group of men near his home, who asked him “Who are you for?” Although not interested in the sport, the man replied, “Wisła.” The attackers, Cracovia supporters, stabbed him to death.
In October 2004, a 17-year-old Wisła firm member was killed in a revenge attack after a knife fight left a Cracovia supporter injured.
On March 12, 2006, following the Wisła-Cracovia Derby match, a group of Cracovia supporters lost one of their flags in a fight against Wisła fans, and subsequently sought out and stabbed a 21-year-old man who succumbed to injuries to his kidney, lung and heart.
One of the most high-profile cases of violence occurred on January 17, 2011, when a 30-year-old man was killed after a Jeep rammed into the back of his silver Audi A4 station wagon and he was beaten and hacked by a gang of over a dozen masked men with baseball bats and machetes. The man, known as Człowiek, was believed to be second in command of Cracovia's "Jude Gang."
In response to the string of murders, subsequent debate has occurred in the Polish press over whether to legalize an unofficial “fighting league” in order to contain football-related violence.
River Plate vs. Boca Juniors
Name: Superclásico Where: Buenos Aires, Argentina
First played in August 1913 - with both sides dominating Argentine football in terms of prestige and support ever since - River Plate and Boca Junior's rivalry is split between River's massive 75,000-seat Estadio Monumental, and Boca's, La Bombonera, which holds just under 50,000.
Joel Richards, author of the e-book Superclásico: Inside The Ultimate Derby, sums up the rivalry as such. "This derby is often pitched as the tale of two cities, the aristocratic River Plate from the north against the people's team, Boca Juniors, in the south. The rivalry in fact started as a turf war in the port area of La Boca in Buenos Aires -- both were founded by the children of immigrants, both had difficulty finding land in the area for their ground, and both chose to have some English in their name to add some perceived glamour to their club. It started out as a local rivalry before they grew to battle out who is the biggest club in the country."
Colloquially, Boca fans have labeled River “Las Gallinas” - "The Chickens" - for their supposed tendency to choke during big games, while River fans have labeled Boca “Los Bosteros,” "The Pieces of Sh*t."
While violence has plagued the rivalry for decades, the contemporary tussles have solidified River and Boca's as one of the fiercest and most dangerous.
In 2013, the superclásico had to be halted in the second half while riot police intervened to stop violence at La Bombonera.
In May 2015, the Copa Libertadores round of 16 match between the two teams was abandoned after four River players were sent to the hospital after being pepper sprayed by fans during the game.
"I can't see, I can't see. I am burning. This is not a war!" River defender Funes Mori was quoted as saying by AFP news agency.
The aforementioned pepper spray incident came after a warning from National Security Secretary, Sergio Berni, who insinuated that he wouldn't ensure the safety of Boca and their fans after the club reportedly were going to allow two notorious hooligans to attend the match, saying "If Boca continues with this stance of admitting these types of violent fans, I have no reason to provide them with security."
For something more lighthearted, check out this year's best, worst and most "WTF" hairstyles at the European Championship.