Vin Ferrara, a former Harvard quarterback, was looking for an aspirin in his medicine cabinet when his eyes fixed upon a ribbed plastic bottle used to squirt saline into sinuses. Ferrara squeezed the bottle, then pounded on it — finding that it cushioned soft and hard blows with equal aplomb, almost intelligence. “This is it,” Ferrara declared. Three years later, Ferrara’s squirt bottle has led to a promising new technology to protect football players from concussions. Football helmets have evolved over more than a century from crude leather bonnets to face-masked, polycarbonate battering rams. But they still often fail to...