Eloise is certainly entering the hitting stage, so in a way I understand the father's frustration. Hitting is apparently part of the developmental stage from 18 to 30 months since children do not yet have the verbal skills to communicate their frustration. When Eloise hits we are quick to say "no hitting" and ask her to use 'nice touch' which we demonstrate by stroking or gently patting her arm. If she persists, we put her on the floor or walk away and let her know that hitting is "not nice and is unacceptable behaviour".
Ask Dr. Sears has some helpful information about hitting and biting in toddlers and their gentle approach to correcting this behaviour makes a lot of sense. Check out 16 Ways to Stop for ideas on how to curb hitting in your toddler.