First, Matt Ryan threw a terrible interception to Marshon Lattimore as the Falcons were attempting to get into field goal range. It resulted in the Saints then having the field goal opportunity at the end of the half after Lattimore returned it to the 29-yard line.
The Saints’ ensuing field goal attempt was good, but it didn’t count because of an illegal formation penalty as time expired.
Josh LeRibeus was not on the line of scrimmage, thus the penalty being called. Because of the penalty, the half ended as time expired when the play went through.
The NFL rulebook (4.8.2b) reads:
If there is a foul by the offense, there shall be no extension of the period. If the foul occurs on the last play of the half, a score by the offense is not counted.
In many cases this season, we’ve seen a 10-second runoff be called in these situations. This, however, was not one of those instances. So even though the Saints had a timeout, they were unable to use it in order to save themselves.