Millions of people are shoved, tripped and held down every day by someone who claims to love them. These acts are considered abusive even if the individual being controlled is not seriously injured. Sadly this form of abuse is often tolerated so long as the damage caused is not visible. Often young boys will wrestle one another, and this is considered normal so long as both parties are okay with the altercation. It is okay, but at times becomes a problem if one person is uncomfortable with it. The problem is exacerbated when excuses are made to justify all behaviors even when it crosses that line. One excuse that I often hear is "boys will be boys". Boys wrestling one another on the playground is fairly standard behavior, but it can cross the line of playful behavior. When it does and nobody enforces the importance of honoring another persons "no", normal behavior can quickly escalate into something very damaging for both parties.
One major problem with the definition of physical abuse is the simple fact that there are times when physical restraint is necessary. Technically restraint is abusive even if it is a necessary evil in a sense. This is one of the main arguments used by many parents with difficult to manage children. While there are some special cases that might change the reasoning behind the restraint, these situations remind us that it is important to evaluate all sides of the situation before making any blanket assumptions.
What makes abuse different than basic physical restraint is the abuser needs to have control as the outcome. An individual using physical abuse in the wrong way would be anyone who is working for personal gain by controlling another person. A police officer arresting an intoxicated driver is using control to protect innocent others from being hurt. A police officer beating a protestor after they have been sufficiently restrained has crossed over the line to using abuse to control the protestor for personal reasons Both situations are physically abusive but the difference can be seen in the reason.
What makes abuse difficult to define and prosecute are similar areas of gray. The only way to sort them fully is to look at intent and listen to the experience from all points of view. This applies even when visual or audio 'evidence' is presented. Sometimes the situation leading up to the altercation defines a different intent than the video or audio clip suggests out of context.