i have never been to brazil but have heard many horror stories about brazilia, sao Paolo and espescially rio, my advice would be to be very very very careful, however by avoiding certain parts of the city you should be fine, which is the same of most latin america cities.
as for football, you are in for a veritable feast, Rio has 4 major teams, vasco de gama. fluminese, botafago and flamengo.
domestically of the four Fluminese are do the best currently lying 4th in serie a, but its an up and down leauge, current copa libetadores champions sao Paolo are in mid table obscurity, and the other 3 rio teams ar having a bit of a shit season fighting off relegation.
Flamengo are the best supported club in Brazil, and they are notorious for being followed by the working class, people actually take the piss if they are losing by chanting there is silence in the favelas. Note you dont want to hang out in the favelas.
Fluminese are seen as the rich club and are followed by the upper classes, whereas vasco de gama are the portugese based side and have a very large black following, they were the first team to play black players.
only vasco has a proper home stadium, the others have crappy little grounds and if its a match of any importance its always played at the maracana.
Excellent.
Well aware of the dangers of Brazil in general, as my colleague got mugged at gunpoint on a previous trip. He's a cocky bastard though so possibly not a fair reflection on the country.
Hopefully there will be a big game during a visit, which I can ask some of the locals I will be working with to take me to.