Suppose a person falls below the legal BAC limit for a state in the
USA (say the limit is 0.08%). Can the person still be charged with a
crime?
Often there is a set of traffic misdemeanors for driving while ability is impaired in fact while under the influence even under the strict liability BAC based grounds for the same offense. Also, in many states, any non-negligible BAC is an offense if the driver is under the age of 21.
Are police officers required to put handcuffs on anyone they suspect
who is under the influence of alcohol?
The decision to arrest and the means by which an arrested suspect is detained are in the discretion of the police officers involved. It is often routine policy to do so, but it is rarely mandatorily required.