Brazilian people are not used to formalitties. They use their first name or - even more often - their nicknames that indentify them better. Other reason for using niknames is to make a very common name a unique name.
Example: The soccer/footbal player Ronaldinho GaÃºcho's, who plays for FC Barcelona, name is Ronaldo de Assis Moreira."Ronaldinho" is dimitutive for "Ronaldo" and that is a simpathetic way to show affection. "GaÃºcho" is everybody who was born in Rio Grande do Sul, a Brazil's state. They use it to identify the place where he comes from.
Example 2: KakÃ¡ - the Milan FC football player - is the nickname of Ricardo Izecson dos Santos Leite. It happens because of the pronounciation of the very common name "Ricardo" in a diminutive way. The second syllabe is "ca" and "Caca" or "Kaka", making his name unique.
And it doesn't happen only in sports. All Brazilian society works like this.
some Brazilian footballers names are hard to pronounce or very long, so they take different names. Sometimes the names sound cooler. or sometimes they do it to avoid confusion. Ronaldinio's real name in Ronaldo, so he took another name to avoid confusion with the other Ronaldo (the Brazilian one, not Chrisiano).
There are many different reasons why Brazillian footballers use nicknames. For some it is a case of their names being far too difficult for many to say. For others they cannot get their names to fit on the back of their shirts. Some Brazillian footballers simply have one name.
because their first name is hard to proniunce
Brazilian have long names like Edison Arentes di Nascimento.
Joe, Anderson, fabiosilva, fabid aurelia
Xabi Alonso, playing for Liverpool in England.
The captain, John Terry.