Declining a penalty is when the team not receiving the penalty turns down the penalty on the other team. Penalties usually result in a loss or gain of yards and a replay of the down.
Example
If the offense runs a play on third down and ends up four yards short of a first down but commits an offensive penalty the defense would most likely want to decline that penalty so that the third down play stands. If they were to accept the penalty the offense would get another shot and making the third down yardage even though it would be 9 yards to go (5 yard penalty) or 14 yards to go (10 yard penalty). Even though the penalty would back up the offense why give them another shot at completing third down yardage. Declining the penalty makes it fourth down with four yards to go and they most likely punt.
No, it is as if it never happened.
yes but the game can only end on a defensive penalty if it is declined by the offensive team
There is no penalty for that
There is no evidence that such a penalty exists in any football league currently.
This penalty is called "Clipping".
No
a penalty
It depends on who made the penalty.
Yes the interception would stand, but no, there wouldn't have been a penalty.
The penalty is a 5-Yard " Delay of Game " penalty
Yes, roughing the passer is a penalty. It calls for a 15 yard penalty on the offending team.
The penalty for an Illegal Forward pass is a five yard spot foul and loss of down. If an Illegal forward pass is intercepted, the penalty would be declined. There would be no enforcement of the penalty.