between Portugal and Greece, when "Jimmy Jump" ran onto the pitch to disrupt the match. Another well known invasion was carried out by Karl Power, who sneaked into Manchester United's team photograph before their UEFA Champions League match with Bayern Munich. His other stunts have involved the England national rugby union team and the British Grand Prix. Rivalries Derby matches, which are matches between two neighbouring rival clubs, are often fiercely competitive. Sometimes there are underlying political or sectarian tensions. The term often applies to matches between two teams from the same city or region, but it is sometimes used to refer to matches between big clubs from the same country. Derbies are usually treated as the most important matches by the fans, players and clubs, regardless of position in the league table, et cetera. The film Green Street embodies the spirit of derbies when one of the characters refers to the West Ham United–Millwall rivalry as that of Israel against Palestine. Of course this film does focus on the mostly past era of hooliganism, however its depiction of matchday passion shows just how important derby day is to fans. When it comes to derbies, the culture of football thrives and shines in all its colours. How Soccer Explains the World is a perfect source into how derbies emerged and what they mean to the community. Supporter groups There are many types of sub-cultures and types of groups centred around football. Casuals are interlinked with hooligan firms. Ultras are a primarily continental European phenomenon (emerging later in Asia, Australia and North Africa), while in South America, the barra bravas (oldest violent organised supporters' groups, emerged in the 1950s in Argentina) are common, with the exception of Brazil, where torcidas organizadas are more prevalent. Players Celebrities Such is the popularity of football that some players become better known for their 'off-the-pitch' activities. The celebrity status is such that advertisers and sports goods manufacturers hire them to sponsor their products. The Brazilian footballer Pelé is such a player. He was so admired as a player during his time that he went on to become a UNICEF ambassador, as well as being a spokesman in advertisements for many different companies. He also spent some time in politics in Brazil. Brazilian striker Ronaldo was chosen as a goodwill ambassador for the United Nations Development Programme in 2000 as he had the highest global appeal