Lack of sales in the hunting and electronics departments accounted for more than half of the decline.
Lower gun sales also contributed to lower sales in departments like outdoor equipment, since fewer hunters were entering the locations, Lee Belitsky, Dick's Sporting Goods' chief financial officer, told The Wall Street Journal.
The newspaper said it was the fifth consecutive quarter that sales were down at the chain.
Dick's company officials made the decision after they found that one of its stores sold a weapon to the Stoneman Douglas gunman, the "Today" show reported.
The gun the company sold was not used in the Parkland shooting, "Today" reported.