In the past, nose rings were a method of controlling bulls because they were dangerous to the handlers. As time went on, it became customary to only use nose rings on bulls led by a halter. Nose rings are unnecessary for bulls that are not led.
One must exercise caution when handling a bull's nose ring. If too much pressure is placed on the ring, it can agitate the bull. The led bull needs to be restrained by the halter around the head. The rope is then fed through the ring. The ring is there to aid in control, and the handler should not depend on it for complete restraint.