I was at a River/Boca derby in 2002. A fan had been stabbed and killed at the previous derby so they were trying to take some of the heat out of this one. Some bright spark decided that parading 40 young kids on the pitch before the match would do the trick. Unfortunately they paraded 20 kids in Boca tops in front of the River fans and vice versa, the poor bairns had coins, fireworks and all manner of other shit launched at them.
At the end of the game the Boca fans lit up some bonfires in the away end (not a clue how they smuggled the wood in). The river officials then brought out these massive fire hoses and blasted any poor sod that was left in the away end.
I was talking to a River fan after the game and apparently they do the same when they go to Boca.
All a bit mad mental