TRIVIAL PURSUITS: What does it mean in football when a penalty is declined?

I was surprised that none could explain it to me in a way I could understand, so I looked it up, and found a great example on www.stilletosetsports.com (with a slight correction pointed out by a PLANSPONSOR reader) that can be useful for those who don’t know as well as those who don’t know how to explain it.

What does it mean when a penalty is declined in an NFL game?

When there is a foul called on one team, the other team has the option of accepting or declining the resulting penalty. For example, let’s say it’s third down and the Cardinals are on the 50 yard line. The Steelers cross the line of scrimmage before the ball is snapped to the Cardinals quarterback (before the play actually begins) and gets a foul for being “offsides.” The Steelers would get a 5-yard penalty—meaning the Cardinals get to move 5 yards closer to the goal and get to redo the 3rd down.

You would think that would be great because the Cardinals move closer to scoring. However, on the play, the quarterback completed a pass 15 yards down the field. If the Cardinals accept the penalty, they would be on the 45 yard line, but it would be the third down. If they decline the penalty, they would be on the 35 yard line and it would be the first down, giving them the opportunity to make more plays.

So, a team will decline the penalty if the play actually puts them in a better position to move down the field and score.