Good question and no, I don't know the answer.
Depends on what is classified as compensatory damages (pain, suffering, loss of use of limb, etc.), and what is punitive damages.
Compensatory damages are tax free - they are 'making whole' the plaintiff in the suit. Since we don't do an 'eye for an eye', compensatory damages are not viewed as income, but just what they suggest they are, compensation for damage incurred, attempting to 'make whole' the plaintiff who suffered the loss. When one receives a payment from an insurance policy (auto, life, even health expenses), the funds are treated as compensatory. Having your health insurance cover a $100,000 medical bill - then to be hit with a tax assessment for that $100,000 - would be a bit much.
Income (net) is always viewed as being 'profit' for who ever receives it. Compensation for damages isn't viewed as 'profit', but rather making up for a sustained loss - thus why it isn't taxed.
Punitive damages are usually treated as taxable income. These damages aren't intended to make whole the plaintiff, but rather to punish the defendant to dissuade from further acts of negligence. The act by the defendant usually needs to have a higher degree of negligence, or willfulness on the part of the defendant, in order for a court to award punitive damages.