Praise be to Allaah.
If these contests between bulls result in harm to the bulls, then they are haraam, because it is not permitted to harm animals or treat them cruelly. But even if no harm is done, these contests are a form of idle entertainment that contain nothing of good or benefit, and are just a waste of time, and buying bulls for the purpose of these contests is a waste of money. In any case, competing for prize money is also haraam.
The ruling on bullfighting is as follows: if the bulls are harmed, or if the contest is for prize money, it is haraam. If that is not the case, it is still a waste of time and money, and it does not befit the decent, wise person to take part in it. We advise our brothers who enjoy these contests and who waste lots of time watching them on TV: time is too precious to be wasted in this idle entertainment that contains nothing of good.(Liqa’ al-Baab al-Maftooh, Ibn ‘Uthaymeen, 52/46). May Allaah bless our Prophet Muhammad.