P was engaged in sparring' at a martial arts studio when his opponent, Susim, punched him in the face. Susim threw 'a light punch' but P stepped into the punch. P, who was 44 years old, was wearing D's 'P2' protective headgear with a clear face mask or shield. The shield hit the bridge of P's nose and cut it. P cleaned the blood from his face and continued to spar with Susim and other persons at the martial arts studio. P saw Dr. Timothy Infuhr, a chiropractor, and said he had been hit in the nose. P complained of pain in the neck, middle back, and left shoulder. Dr. Infuhr diagnosed a muscle spasm affecting the neck's C3 vertebrae. He could see the 'tightness of the [neck] muscle.' Dr. Infuhr 'adjusted' the C3 vertebrae, but it did not have the desired effect. He also adjusted the C1 and C2 vertebrae. Dr. Infuhr understood that '[t]here can be a risk' that chiropractic manipulation of the neck will cause a dissection of the carotid artery. He opined that he had not done anything of 'sufficient magnitude . . . to cause any damage to the carotid artery.' He did not detect 'any signs or symptoms of [a] possible stroke.' Dr. Infuhr had been 'trained to detect symptoms of strokes in patients.' The next morning at about 4:00 a.m., P suffered a stroke caused by a dissection of the carotid artery. The stroke resulted in severe brain damage. P 'needs a caregiver at all times.' Ps sued D in product liability. Several expert witnesses testified at the trial. Dr. Harris Fisk, a neurologist opined that the dissection was due to the punch in the face. Dr. Fisk further opined that the chiropractic manipulation did not have a significant impact on the dissection. There was no 'persuasive medical evidence' that the manipulation 'could . . . have taken a situation which is already in progress and made it worse.' Dr. Pressman, a neuroradiologist opined: 'the more likely cause [of the dissection], and the most probable so I'd say more than 50 percent likely, is the blow to the head.' Dr. Pressman testified: 'The carotid dissections we see are usually . . . spontaneous [in origin]. We see a number of those, particularly in young people, and traumatic [dissections].' Dr. Amos, a neurologist, opined that although it is possible that the punch to P's face caused the dissection, 'there's an equally strong case to be made for the chiropractic manipulation.' '[I]t's a known risk for carotid dissection to undergo a cervical or neck manipulation.' Such manipulation was probably the cause of about half of the carotid artery dissections in Dr. Amos's patients. Dr. Amos was not aware of any report in the medical literature of a blow to the face causing a carotid dissection. The dissection also could have been 'a spontaneous event' that had nothing to do with the punch or the chiropractic manipulation. A spontaneous dissection is 'without a particular known cause or in[ci]ting event' is seen in 'upwards of one half' of the dissections that Dr. Amos had seen, 'no actual cause or force or injury has ever been documented.' Dr. Amos opined: '[It is not clear that any of these [three] factors [i.e., the punch to the face, the chiropractic manipulation, and the possibility of a spontaneous dissection] outweighs the others. So I've given them a one-third, one-third, one-third probability.' Dr. David Dainty, respondent's expert in the 'biomechanics of injury,' opined that to cause a dissection of the carotid artery, a punch to the face would have to be of 'such force' that it would be 'directed almost through the person' so that the neck would be bent 'past the physiological range.' Dr. Dainty further opined that (1) P's carotid dissection 'could not have been prevented by the use of any helmet,' and (2) 'to a high degree of scientific probability . . . it's not likely' that the Century P2 headgear 'played a role in causing the . . . stroke suffered by [Phillips].' D's Vice-President of Operations testified that D has sold about 105,000 units of the Century P2 headgear. Ps' claim 'is the only claim of injury ever made.' The jury returned a special verdict by 10 to 2 in favor of D. Ps appealed.