The stock market continued its impressive rally on Tuesday morning, with many popular market benchmarks hitting new all-time highs. Although concerns about the coronavirus outbreak persist, testimony from Federal Reserve chair Jerome Powell gave investors confidence that the disease wasn't yet having a major impact on monetary policy. As of 11 a.m. EST, the Dow Jones Industrial Average (^DJI 0.06%) was up 123 points to 29,400. The S&P 500 (^GSPC -0.22%) rose 22 points to 3,374, and the Nasdaq Composite (^IXIC -0.52%) picked up 83 points to 9,711.

Among individual stocks, Sprint (S) and T-Mobile US (TMUS 0.47%) got long-awaited good news that sent their shares soaring. However, Under Armour (UA 0.95%) (UAA 0.92%) wasn't so lucky, as investors reacted negatively to earnings.

Sprint wins

Shares of Sprint soared 73% after the wireless carrier and its would-be acquirer, T-Mobile, got a key court victory. The ruling set the stage for the merger between the two carriers to go forward.

Laptop with Sprint logo on the back, with bushes behind.

Image source: Sprint.

A federal judge ruled that Sprint and T-Mobile could move forward with their $26 billion deal, saying that the combination wasn't particularly likely to have anticompetitive impacts in the U.S. wireless telecom market. The judge seemed compelled by the innovative spirit that T-Mobile has brought to the industry, and the ruling contemplates T-Mobile's continuing to offer changes that could in fact be of benefit to consumers.

For a long time, the outcome of the deal seemed to be in doubt, as arguments from state attorneys general hinged on the idea that reducing the number of available major carriers in the U.S. from four to three would necessarily put more pricing power in the hands of fewer participants. Sprint stock in particular had slumped as time went by, seemingly indicating that the deal wouldn't go forward.

Now, though, the two companies are down to some small details before finalizing their merger. With T-Mobile shares up more than 10% as well, shareholders are excited about what the new T-Mobile could bring to the U.S. wireless market.

Under Armour sees tougher times ahead

Shares of Under Armour were down 16% as investors grappled with concerns in the company's fourth-quarter financial report. Recent results weren't as good as anticipated, and the athletic apparel specialist's outlook raised a new issue for the future.

Under Armour's fourth-quarter results were mixed. Sales climbed 4% to $1.44 billion, but that wasn't as high as investors had expected. Under Armour posted a modest loss for the period, reversing year-ago profits and surprising shareholders. Despite past efforts, Under Armour has more to do, and CEO Patrik Frisk believes that "ongoing demand challenges and the need to drive greater efficiencies in our business requires us to further prioritize our investments" as it goes forward with a new restructuring initiative.

The coronavirus will also hurt Under Armour in 2020, with a current hit of $50 million to $60 million from sales in China as a result of the disease. It's entirely possible that further downgrades of guidance will come in the future, given the uncertainty surrounding the outbreak. Overall, Under Armour expects a low-single-digit percentage decline in revenue, with a larger drop in the key North American market.

Under Armour has already had to deal with strong competition in the athletic apparel and footwear space. With even more challenges coming up from China, shareholders seem far from certain Under Armour will eventually win the race against its rivals and regain its status as a top growth stock.