"Limitations on Reviewable Plays
ARTICLE 7. No other plays or officiating decisions are reviewable. However, the replay official may correct obvious errors that may have a significant impact on the outcome of the game, including those involving the game clock, whether or not a play is reviewable. This excludes fouls that are not specifically reviewable (See Article 8, following)."

Think that play had a significant impact?
and...

"On running plays, there are several situations where replay can get involved.
•The first situation is wether a player made the line to gain or not, either for a first down or the goal line. If the runner is ruled down or his forward progress is stopped replay can review that spot in relation to the line to gain. If the line to gain is not involved then that spot is not reviewable."

The ball did not make the line to gain.