What: Shares of fast-casual chain Potbelly Corporation (NASDAQ:PBPB) got swept up in the malaise hitting the fast-casual dining sector last year, finishing 2015 down 11%, according to data from S&P Capital IQ.

As the chart below shows, it was a rocky year for the stock -- and when the closing bell came, it was down for the year.

PBPB Chart

PBPB data by YCharts

So what: Potbelly's roller-coaster ride began in February when the chain beat fourth-quarter earnings estimates, rising 17% after a strong report. The company posted a profit of $0.06 a share, twice what analysts had expected, and the company forecast 20% growth in its bottom line for the full year. Short-covering may have also driven the single-day spike as the stock quickly fell over the subsequent days. Later that month, the stock fell 7% in a single day after the company's CFO unexpectedly resigned to take a position at a different company. Investors sometimes interpret such a move as a sign of something awry, or, at the very least, a lack of insider confidence in the business.

The stock hummed along for the next few months before diving on its second-quarter earnings report on Aug. 5. Shares dropped 12% as its per-share profit of $0.08 missed estimates of $0.10. Rising food costs ate into the company's bottom-line profit as well, a concern that is facing restaurants across the board. 

Now what: Potbelly finished out the year relatively evenly, and an 11% drop is still better than some of its peers suffered as the recent onslaught on restaurant stocks prompted a sell-off this year. The stock was relatively unchanged following its third-quarter earnings report in November as same-store sales ticked up 3.7%. Looking ahead to 2016, growth will continue to be driven by new store openings. With a forward P/E of 35, the stock could come under pressure if it misses the reasonable earnings targets that analysts have set.