5 of Last Week's Biggest Losers

There's never a shortage of losers in the stock market. Let's take a closer look at five of this past week's biggest sinkers.

Source: Barron's.

Let's start with Northern Dynasty Minerals. The minerals explorer plunged on Monday after revealing that its cash-rich partner, a subsidiary of London's Anglo American, is withdrawing from the company's Pebble copper mine project in southwestern Alaska.

The move will leave Northern Dynasty as the sole owner, but that's not as savory a proposition as it may sound. Anglo's subsidiary had already invested $540 million on the copper project, and it had to bump that investment to $1.5 billion to bankroll project costs if it wanted to retain its 50% stake. By walking away, it's essentially saying the project is too risky for its return on investment.

Redbox parent Outerwall also took a hit this past week after hosing down its outlook. The company that recently changed its name from Coinstar is now expecting a profit of $0.82 to $0.94 a share on $569 million to $589 million in revenue for the quarter that comes to a close this month. That's a far cry from its earlier guidance this summer calling for at least $1.36 a share in earnings and $604 million in revenue.

Customers are returning DVDs sooner, and Outerwall finds itself having to promote its disc-firing rental kiosks more aggressively. Outerwall's new guidance for the entire year suggests that the holiday quarter will also be challenging.

BlackBerry's world came crashing late into Friday's trading day, when the smartphone pioneer revealed that it will post a massive quarterly loss and lay off 4,500 employees. Scaling back its operations as it seeks strategic alternatives may have a happy ending if a suitor does show up, but for now the market's bracing for the worst.

Rockwell Medical fell every single trading day last week, giving back most -- but not all -- of the gains it registered on Friday of the prior week, when it rocked higher on encouraging results on its potentially promising iron replacement therapy for chronic disease patients on dialysis. Volatility comes with the territory when we're talking about small medical companies, where a single product can really move the needle.

Finally we have Polypore pouring on the losses after a cautionary note by the otherwise bullish analysts at William Blair. Polypore has become a popular stock for investors betting on increasing demand of electric cars, since it makes microporous membranes incorporated in lithium battery solutions.

William Blair is sticking to an "outperform" rating on the stock, but it noted concern about the slow pace at which consumers are embracing vehicle electrification.