The Court held that because Harris started the high-speed car chase, creating a dangerous situation that threatened the lives of innocent bystanders, it was reasonable for Scott to try to stop it even when it put Harris in danger of serious injury. To reach that conclusion, the court first had to decide the factual issue of whether Harris' behavior endangered human life.
Harris argued that his driving was controlled and nonthreatening and that his path was clear of other traffic and pedestrians. His arguments were successful in the Court of Appeals, but after viewing the police videotape of the chase all but one of the Supreme Court Justices disagreed with the appellate court. The Supreme Court concluded that Harris' driving did pose an immediate threat to the lives of others.
On the question of whether the force used was "reasonable," Harris argued that to be reasonable Scott's attempt to stop the chase using force must meet standards set forth in Tennessee v. Garner, 471 U. S. 1. There, a police officer shot an unimposing, unarmed burglary suspect in the back of the head as the suspect fled. The Garner court held that the officer's use of deadly force was not reasonable because (1) the suspect did not pose an immediate danger to others, (2) the deadly force was not necessary to prevent the suspect's escape, and (3) the officer gave no warning.
The Scott majority rejected Harris' Garner arguments. They held (1) that Garner did not establish any across-the-board test for determining the reasonableness of Fourth Amendment seizures, and (2) that it was distinguishable on the facts. In both Garner and the case before it, the Court applied the standard Fourth Amendment "reasonableness" test to the circumstances of that case. Was it objectively reasonable for Scott to do what he did?
Looking to the circumstances of the car chase, the Court held that it was reasonable for Scott to take the actions he did. Moreover, the majority noted, if the Court were to rule otherwise -- in effect, requiring police to let speeding suspects get away -- it would give criminals an incentive to drive recklessly just so the police would have to break off pursuit.