It all went down during a festival in Caparroso, Spain -- when the bull entered the ring and seemed to know its own fate ... ultimately deciding it was better to make a break for it.

We should say ... it's unclear if the event was a proper bullfight or a rodeo-style thing (without the matador and the stabbing), but what we do know is these things don't typically end well for the bull.

The bull lept over a wall and into the crowd before charging out of the stadium and onto the streets -- where spectators began running for their lives (oh, how the tables turned!).

The local mayor says the bull was eventually captured -- though its fate is unknown.

As we previously reported, a different bull went after a matador during a bullfight in Spain last month -- goring the dude in the groin before he was eventually killed.