In most states, if a dog was provoked in some way, the owner (the defendant) will not be found liable to the person bit by the dog (the plaintiff). This rule may be limited by a state's "dog-bite" statute, but it is rarely eliminated altogether. The provocation defense and its exceptions are discussed in this article.
When someone hears the word "provocation," teasing or poking or being mean to a dog is what typically comes to mind. While that kind of behavior counts as provocation, other unintentional actions can also lead to a provocation defense.
For example, if a plaintiff is bit after stepping on a dog that he or she did not see, the defense could be available even though the plaintiff technically did nothing wrong. The key is that something happened to the dog to make it behave aggressively.
Although referred to as a defense, technically in most cases the plaintiff must prove, as part of his or her case, that the dog was not provoked. The plaintiff cannot "conveniently" leave out facts, and he or she must convince the judge or jury that it was more than 50% likely the dog was not provoked (under the "preponderance of the evidence" burden of proof in civil cases) . The defendant can then argue that the plaintiff failed to prove the dog was not provoked, either by arguing why the plaintiff's evidence is weak or by presenting new evidence.
While the law does not talk about a "reasonable dog" standard of behavior, that standard is implied when applying the provocation defense.
If an overly sensitive dog reacts in an overly aggressive manner to a slight provocation, the defendant (the dog owner) will likely be held liable. What is important is whether it was foreseeable or predictable that the dog would be provoked under the circumstances. Therefore, all of the circumstances surrounding the attack matter. For example, if the dog is a known aggressive breed and is eating when the plaintiff puts her hand near the dog's face, a judge or jury might find that the dog was provoked.
Keep in mind, however, that if the defendant knows his dog is more aggressive than people might expect, he is under a duty to keep people safe from the dog. That means the provocation defense is less likely to be successful if the circumstances were such that the defendant should have warned the plaintiff or otherwise made the situation safe.
About half the states have dog-bite statutes. The statutes vary from state to state (you can find them here), but they all essentially make it easier for a plaintiff to win a dog-bite case. However, the provocation defense is not simply eliminated in states with dog-bite statutes.
In many states, the courts have made it clear that even though the dog-bite statute appears to make a defendant liable so long as his dog bit the plaintiff, the plaintiff can have her damages reduced or lose the case entirely if she "contributed" to the bite by provoking the dog.
Some dog-bite statutes specifically include the provocation defense. For example, the first sentence of the Illinois dog-bite statute reads: "If a dog or other animal, without provocation, attacks, attempts to attack, or injures any person . . . ."
Some dog-bite statutes have specific provisions addressing the kind of provocation. For example, in Florida the plaintiff must have been acting "mischievously" or "carelessly" for the provocation defense to apply.