Negligence per se is conduct that violates standards of care as established by statute or law.
Depending on state law, violating a statutory standard of care can be interpreted as (1) conclusive proof of negligence, making the defendant automatically liable without giving the defendant a chance to explain their actions; (2) presumptive proof of negligence, making the defendant liable unless the defendant can rebut the presumption of negligence by explaining the reasons for their actions; or (3) evidence of negligence, which can be considered when deciding whether the defendant should be liable at all.