The stock market gained ground on Thursday, but the rise in major market benchmarks was modest at best. The Dow finished up just 15 points after having been higher by as much as 100 points earlier in the session, as investors appeared to grow more cautious despite ongoing signs of economic strength domestically. Many market participants looked at the critical meeting between political leaders of the U.S. and China in Florida as an indicator of future trade relations and potential geopolitical conflict going forward.

Yet even though the market was relatively comfortable with the day's events, some stocks weren't as lucky. Advanced Micro Devices (AMD 1.34%), Plug Power (PLUG -0.77%), and Banco Santander Brasil (BSBR -0.52%) were among the worst performers on the day. Below, we'll look more closely at these stocks to tell you why they did so poorly.

AMD deals with a negative analyst call

Shares of Advanced Micro Devices dropped 6% after getting a poor rating from analysts at Goldman Sachs. The Wall Street behemoth initiated coverage of the chipmaker with a sell rating, setting a price target of $11 per share, which remains more than 15% below current levels even after today's drop. Analysts argued that AMD's success is unlikely to last because of potential competitive threats from other major players in the space, and Goldman believes that the current share price assumes that AMD will be particularly effective in claiming key wins in the years to come. Anything short of that rosy scenario could hurt the stock, and investors seemed inclined to agree, based on today's trading. That said, even with the drop today, AMD stock is up by more than 400% from its worst levels over the past year, giving longtime investors plenty of gains despite the pullback.

AMD Radeon chip.

Image source: AMD.

Plug Power gives back some gains

Plug Power stock fell 5%, retreating only very slightly from the better-than-70% gains that the fuel cell specialist enjoyed in Wednesday's session. Those gains stemmed from an agreement that Plug Power made with online retail giant (AMZN -0.36%) to use fuel-cell and hydrogen-powered equipment and technology in its fulfillment network. In particular, Plug expects to sell its GenKey charging systems to make Amazon's operations more energy-efficient and cut related costs. Plug Power CEO Andy Marsh termed the deal "a tremendous opportunity for Plug Power to further innovate and grow while helping to support the work Amazon does to pick, pack, and ship customer orders," and even those investors who made a lot of money in the stock's run-up on Wednesday chose not to take too much of their profits, anticipating even bigger future gains.

Banco Santander deals with an investor's sales

Finally, shares of Banco Santander Brasil fell 6%. The Brazilian unit of the financial giant is having to endure the sale of a portion of a major shareholder's stake in the company, with Qatar Investment Authority's sale of 80 million units of the bank expected to fetch prices that were below what most of those following the stock had hoped to see. Some believe that the hesitation among buyers in the offering stems from the impressive gains that the Brazilian financial institution's shares have seen over the past year and half, which have amounted to a doubling of the stock price. Predictably, the stock has lost ground since the Qatari sovereign wealth fund announced the offering, but once it's complete, some expect Banco Santander Brasil to return to solid performance as long as the Brazilian economy remains on a recovery track.