Which activity is NOT classified as a crime under the Welfare and Institutions Code 5150?

The activity that is not classified as a crime under the Welfare and Institutions Code 5150 is mental health detention. Under this code, individuals may be taken into custody for mental health evaluation if they are deemed to be a danger to themselves or others due to a mental disorder. This detention is a protective measure rather than a criminal charge, focusing on the individual's need for mental health treatment rather than punishment.

In contrast, possession of a controlled substance, being under the influence of drugs, and reckless driving are all actions that are typically defined as crimes under various sections of law and carry potential legal penalties. Mental health interventions under the Welfare and Institutions Code aim to provide care and support rather than imposing criminal consequences.