What mistakes hurt a reining score the most?

The mistakes that hurt a reining score most severely are formal penalties for specific errors, followed by minus maneuver scores accumulated across the pattern, and then the cumulative effect of a horse that appears unwilling, resistant, or difficult to guide throughout the run. Formal penalties are the most immediately damaging because they add a fixed deduction to the final score regardless of how well the remainder of the run is performed. Missing a lead change, over-spinning or under-spinning, breaking gait in a circle that requires loping, going off-pattern, failing to complete a required maneuver, or exhibiting obvious disobedience all carry specific penalties that can erase the value of plus maneuvers elsewhere in the run. Incorrect pattern execution — performing the maneuvers in the wrong order, in the wrong location, or missing a required element entirely — carries significant penalties that reflect the importance of pattern accuracy in judged competition. A missed lead change, which is one of the most commonly penalized errors, represents a clear failure of one of the most visible and technically demanding elements of the run and draws the judge's attention to the quality of the horse's training in a way that affects the perception of the entire run. Beyond formal penalties, the maneuvers that most directly affect the overall score are those that appear in every reining pattern: circles, stops, and spins. A horse that earns minus scores consistently across all three of those elements can end a run with a significantly reduced score even without any formal penalties. Resistance and disobedience — obvious throughout the run rather than isolated to a single maneuver — affect the judge's overall impression and the willingness credit that plus maneuvers require, making it difficult to earn plus scores elsewhere even when individual maneuvers are technically executed.