An NFL snap is legal only when it starts from the ground, travels backward in one quick continuous motion, and goes to an eligible backfield receiver. Here is how officials rule it.

A blocked punt can stay live behind the line but dies on a kicking-team recovery beyond it. Here is how location and touching decide possession.

A motionless loose ball is not instantly dead. NFL Rule 7-2-1(i) tells officials when to wait, whistle, and award possession.

An ordinary NFL kickoff that first touches short of the receiving 20 is dead immediately. Learn why the ball usually goes to the 40 and when exceptions apply.

A score ends an NFL play at a precise legal moment, not when the whistle sounds. Here is how the trigger changes for touchdowns, field goals, safeties, touchbacks and Trys.

A football that hits an inbounds NFL official stays live. Here is how the rule changes for passes, fumbles, kicks, boundaries and overhead equipment.

The NFL now requires identical stadium video-board treatment for both kicking teams on field goals and extra points, closing a loophole highlighted by a Patriots optical-illusion claim.

NFL punt gunners may release immediately, but most linemen must stay within one yard of the line until the kick. Here is the five-yard rule.

An NFL scrimmage kick must occur on or behind the line. Here is how the rule treats punts, field goals, blocked kicks and rare second kicks.

NFL penalties during a fumble or backward pass usually start from the loose-ball spot. Here is how the basic spot, three-and-one rule and key exceptions work.

An NFL forward handoff is legal only behind the line of scrimmage to an eligible receiver. Learn the penalties, live-ball fumble rule and key exceptions.

Most fouls before an NFL forward pass ends are enforced from the previous spot, but grounding, pass interference and personal fouls create major exceptions.

An eligible receiver who goes out of bounds usually loses eligibility for that pass. Learn the reestablishment test, forced-out exception and loss-of-down penalty.

NFL offensive pass interference explained: push-offs, pick plays, early downfield blocks, the one-yard boundary, key exceptions and the 10-yard penalty.

A defender may block some attached eligible receivers low at the line, but a flexed receiver is protected everywhere. Here is the NFL's two-yard test, penalty and key exception.

NFL defensive pass interference begins when the ball is thrown and ends when it is touched. Learn the prohibited acts, legal contact, spot penalty, exceptions and head-turn myth.

A fair-catch signal can kill a punt when any receiving player gains possession—not only the returner who waved. Here is how valid, invalid, muffed and touched kicks differ.

Learn when an ineligible receiver can touch an NFL forward pass, the five-yard penalty, why the ball stays live, and how a tip changes eligibility.

NFL pass eligibility starts with alignment, number and reporting status. Learn who can catch, how tipped passes change eligibility and the forced-out exception.