Wall Street finished the week on a relatively quiet note, as gains early Friday for the major market indexes evaporated on fresh tariff concerns, leaving the benchmarks essentially flat for the day. For the most part,  market participants seemed content to wait for corporate America to weigh in on the state of the U.S. economy when earnings season starts up a month from now.

However, while political and macroeconomic factors always have the capacity to move markets, some high-profile company-specific news also weighed on overall sentiment Friday. Westinghouse Air Brake Technologies (WAB 1.00%), NiSource (NI 0.27%), and Opko Health (OPK 1.54%) were among the day's worst performers. Below, we'll look more closely at these stocks to tell you why they did so poorly.

Wabtec gets some cautious views

Westinghouse Air Brake Technologies lost 13% in the wake of cautious comments from Wall Street analysts. Stock watchers at JPMorgan weighed in on the proposed merger of Wabtec and General Electric's (GE -0.76%) transportation division, suggesting that early estimates of the financial impact of the deal might have been too ambitious. Wabtec has already started to raise capital to put itself in a position to move forward with the deal, but the negative comments sapped some of what had been an impressive gain of more than 50% for the company's shares since February.

Air brake coupler overhaul in a workshop.

Image source: Wabtec.

NiSource deals with Boston-area fallout

NiSource dropped 11% in response to Thursday night's series of natural gas explosions in three different suburbs north of Boston. One person was killed by the blasts, many more were injured, and thousands of the utility's natural gas customers have been forced to leave their homes. Investigations into the cause of the explosions haven't yielded anything definitive yet, but for investors who had thought that the utility sector was a quiet place to put capital and earn a reasonable dividend yield, the past 24 hours have been a reminder that there's risk in every sector of the stock market.

Opko reopens for trading

Finally, Opko Health fell 10% after the stock resumed trading on the Nasdaq Friday, a week after it was halted following news of an SEC civil lawsuit against the company. The regulatory agency included Opko CEO Phillip Frost and the company in a suit alleging the use of pump-and-dump schemes, wherein buyers purchase a stock, tout the company through illegal promotions and manipulative trading tactics, and then sell it while the price is artificially high. With the reputation of its CEO seemingly tarnished beyond repair, investors are less confident about Opko's ability to find success in its core healthcare operations.