From Longman Dictionary of Contemporary Englisha slap on the wrista slap on the wristPUNISHa punishment that you think is not severe enough → slap
Examples from the Corpus
a slap on the wrist• They just gave him a slap on the wrist then and that enabled him to go out and kill my husband.• So instead of a slap on the wrist I got promoted to high-flying executive symptoms.• In the past, officers who mistreated prisoners often received a mere slap on the wrist.• The fine was so low, it was little more than a slap on the wrist. 