Reviewable Plays in the NFL

If an offensive guard puts his hands on an onrushing tackle, the official uses his judgment to decide whether the contact is holding. The call is not reviewable. If a pass receiver lands with only one foot in bounds, it's clear to anyone that the pass should not count as completed. There, a review can clearly expose whether an official was correct.

NFL rules are complicated, and they're frequently tweaked and revised. Basically, there are three types of reviewable plays:

Calls involving sidelines, goal lines and end line. This includes whether a runner broke the plane of the goal line, whether a player stepped out of bounds, whether a player recovered a loose ball in or out of bounds, or whether a loose ball hit the sideline
Calls involving passes. When the ball was knocked loose, was the player passing or was it a fumble? Was a pass completed or intercepted? Did an ineligible player touch a forward pass? Did a player cross the line of scrimmage before passing?
Other detectable issues. Was a runner down by contact prior to fumbling? Were there more than 11 players on the field at the snap? Was the ball spotted correctly when a first down was at stake? Was a kick that passed the goalpost lower than the uprights successful?

[sources: Sando, Oldfather].

The review rules specify a number of situations that are not reviewable. These include:

All judgment calls, such as pass interference, holding and roughing the passer
A play where a runner is ruled down by defensive contact, not involving a fumble
The recovery of a loose ball in the field of play
Inadvertent whistles and down calls

Time on the clock can only be reviewed at the very end of a half. Kick attempts can't be reviewed if they sail higher than the uprights.

Some reviews have not only changed games but helped change what's reviewable. During the final seconds of a Browns-Ravens game in November 2007, Cleveland kicker Phil Dawson booted a 51-yard field goal. The ball hit an upright, ricocheted off the goal-post gooseneck and sailed back toward the field. The officials first ruled the kick no good, but the replay clearly showed the ball had gone through the goal. At the time, field goals were not reviewable, but the referee reversed the call anyway (he claimed the replay wasn't a factor). The Browns tied the game and won in overtime. Later, a new rule was added -- known as the Phil Dawson Rule -- and certain field goals are now reviewable [source: DeTullio]

For most of the game, a coach's challenge is needed to start the review process. Read on to find out how this works.