Under Armour Inc.’s two share classes in the S&P 500 Index are parting company on price. A gap between the athletic-wear maker’s voting Class A stock and non-voting Class C swelled Wednesday to 19.7% after fourth-quarter results came out, according to data compiled by Bloomberg. The spread was the widest since December 2016 and surpassed those for the S&P 500’s other four dual-class companies. Discovery Inc. came the closest, at a 17.3% spread between voting and non-voting shares. Gaps at Alphabet Inc., Google’s owner, and News Corp. were less than 0.5%. Fox Inc.’s voting shares were 4% cheaper.