Two weeks ago in an NFL game between the Cowboys and Raiders, referee Gene Steratore used an index card to measure a first down. The Washington, Pa. native could probably do something similar with the Penguins these days, to accurately gauge their margin for error. Scoring goals has officially become an issue for the Penguins, who are tumbling toward the bottom of the NHL in goals per game (2.73). As a result, it has forced them to pretty much play a flawless 60 minutes when it comes to other aspects of their game, and they did not do that during a 4-1 loss to the Red Wings Sunday at Little Caesars Arena. “You might have to win a 2-1 or 1-0 game when it’s not going in as easy for you,” Crosby said. “We have to understand that and make sure that if it isn’t going in easy for us, we don’t hurt ourselves with mistakes when we’re not scoring as much.” The mistakes the Penguins made were mostly in the neutral zone, coach Mike Sullivan said, and they involved how the Penguins handled the puck. On another night, that itself might turn into a concern, but it’s hard after this one to fret about anything other than the Penguins offense. Specifically the lack of it. They’ve been held to two or fewer goals in seven of their last 12 games, with only four wins in the bunch.