A slump in chicken wing prices has Sanderson Farms (SAFM), one of the nation’s biggest poultry producers, wondering aloud if the player-protest controversy in the National Football League might be to blame.

“The only thing puzzling me right now is wings,” Joe F. Sanderson Jr., chief executive officer of the namesake company, said Thursday on a conference call to discuss earnings.

“It’s just been reported to us that some of our customers think that their traffic is down because of the demonstrations by some of the NFL players,” he said in a telephone interview after the call.

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Wings had a banner year for much of 2017, boosting profits at processors like Sanderson. But spot prices slumped in each of the last three months and are now 14% lower than a year earlier, according to one U.S. government measure. Amid the NFL dispute, it’s unclear where prices are headed from here, Sanderson Jr. said.

Food sellers have differing views on how much impact player protests during the national anthem at NFL games have had on revenue. Last month, Papa John’s International (PZZA) said the NFL flap was hammering pizza sales, but Wingstop said it hadn’t seen any impact from waning football viewership.

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Sanderson shares fell 13% to $145.85 Thursday in New York, the worst slump since August 2004. The company posted lower-than-expected earnings per share in the fourth quarter as chicken prices weakened from rising production and hurricane-related disruptions. Rival processor Pilgrim’s Pride (PGPDQ) dropped as much as 8.1%, the most in almost 13 months, while Tyson Foods (TSN) fell 2.5%.

Demand for chicken wings usually surges during the Super Bowl. Americans were projected to eat 1.33 billion during last year’s game, according to the National Chicken Council. The championship this season will be on Feb. 4.

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While the NFL is an easy target, it’s likely not the only cause of the drop in prices.

Increasing substitution of boneless wings is also cutting into chicken-wing demand, Sanderson said. Buffalo Wild Wings (BWLD) in October announced cost-cutting efforts that included selling more boneless wings to sidestep a surge in the traditional variety.

Boneless chicken breast prices are expected to rebound early next year like usual, as consumers aim to eat lighter foods after the holidays and retailers run promotions on the cut, according to Sanderson.