Another older decision, I like warrantless entry cases so...
Police in Utah responded to a call of a loud party. From outside the house, officers witnessed a physical fight between a drunk juvie and some adults in the kitchen. An officer opened the door and announced his presence, but no one noticed. So the police went into the house to deal with the fight. Several people were arrested and charged with contributing to the delinquency of a minor.
At trial, the court suppressed all evidence after the police entered the house, holding that the entry violated the Fourth Amendment. The court held that the injury caused in the fight (the juvie punched one of the adults in the mouth, causing him to bleed) was insufficient to trigger the emergency aid exception, and also that after making entry the officers acted in an enforcement capacity rather than rendering aid. And the trial court held that there were no exigent circumstances.
The Supreme Court held that the police were confronted with ongoing violence within the house, and that satisfied the exigent circumstances requirement. Given that people in the house were currently fighting, the Fourth Amendment does not require officers to wait until someone is badly hurt before they take action. The Court also pointed out that an officer's subjective intentions are irrelevant to Fourth Amendment Analysis, so it didn't matter whether the officers intended to make arrests or patch up a nosebleed. All that matters is whether or not the entry was objectively reasonable, and in this case is clearly was.
The concurring opinion in this case is amusing to read.