There are two main arguments against the sport. Firstly that it is cruel and secondly that it inflicts pointless suffering on the animals involved.
Those against say that the odds are stacked against the bull and that the sport is cruel and evil.
Even though the death of the bull isn't shown in Portugal, the bulls are nearly always killed. Each year there are about 300 fights and around 2,500 bulls are killed in Portugal.
Animal rights campaigners claim that in Spain 30,000 bulls are killed in the ring each year.
Horses ridden by the cavaleiros also suffer, as they get injured when they clash with the bulls.
The fights can be dangerous and matadors have been killed during bullfights. One of the most famous bullfighters in history, Manolete, was killed in 1947.