Biggest Stock Movers: Shake Shack Sizzles; Roundy's Retreats

Plenty of stocks go up and down in any given week. The gainers inspire us to keep investing. The decliners keep greed in check while reminding us about the risks of the equity markets.

Let's go over some of last week's best and worst performers.

Shake Shack (SHAK) -- Up 34 percent last week

The fast-growing burger chain soared on reports that a related entity has taken out a trademark for the Chicken Shack name. Shake Shack has plenty of room to grow as a burger chain, but if it's launching a sister concept specializing in poultry -- likely chicken sandwiches -- it can make things even more interesting for one of the hottest IPOs of the past year.

Red Robin Gourmet Burgers (RRGB) -- Up 18 percent last week

Shake Shack wasn't the only burger flipper slinging some serious lettuce last week. Red Robin also moved higher after the table-service restaurant chain posted better-than-expected quarterly results. Red Robin clocked in with a profit of $1.10 a share, well ahead of the 88 cents a share that analysts were forecasting.

It's a strong showing for a company that has fallen short of Wall Street profit targets in two of the three previous quarters.

MannKind (MNKD) -- Up 13 percent last week

An upbeat analyst report on MannKind helped send the biotech higher. MannKind recently began marketing Afrezza, an FDA-cleared inhaled insulin. It's naturally a potential breakthrough for diabetics tired of needle pricks, but it's been off to a slow start. Jefferies & Co. analyst Shaunak Deepak put out an encouraging report, arguing that a lack of education could be the problem. Deepak discovered that more than a third of the doctors treating patients with diabetes don't know about Afrezza, but those who are familiar with the inhaled insulin are actively prescribing it.

Roundy's (RNDY) -- Down 25 percent last week

The New York Stock Exchange's biggest sinker last week was Roundy's, shedding a quarter of its value after going through with a highly dilutive secondary offering. The struggling grocery store operator priced 3.5 million shares at $3.50. The problem with the pricing is that the operator of 150 supermarkets and 100 pharmacies had its stock kick off the week at $4.76. Things have to be desperate if underwriters have to offer such a big discount.

hhgregg (HGG) -- Down 15 percent last week

Consumer electronics retailer hhgregg took an 18 percent hit a week earlier after posting a big year-over-year decline in sales for its most recent quarter. Instead of bouncing back last week, the selling continued to the tune of an additional 15 percent drop. The new week got off to a bad start when UBS downgraded the retailer to "sell" as it slashed its price target to $4.

Southwest (LUV) -- Down 12 percent last week

Sometimes what's good news for consumers is bad news for the market. Shares of Southwest went on a sharp descent after its CFO announced that the air carrier will grow its capacity by as much as 8 percent this year. Its earlier guidance was calling for an uptick of just 7 percent in available seat miles.

Increasing capacity for the airline industry concerns the market because it can eat into pricing. If too many carriers are trying to fly more, it can result in cutthroat fares. That's great for consumers, but the air carriers won't like what that does to the bottom line.

Motley Fool contributor Rick Munarriz has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. Check out our free report on one great stock to buy for 2015 and beyond.