Two feet in the NFL. One foot in college.

Identical throw, identical catch, identical sideline. Two different rulings, depending on which league is playing.

The rule

College football requires one foot in bounds. The NFL requires two — or an equivalent body part, such as a knee or the back of the thigh, touching down in bounds.

And the NFL version is stricter than it sounds. Two taps of the same foot do not count. Both feet have to touch down separately.

Two taps of one foot is not a catch. It has to be both.

What it changes

• 01Sideline catches look routine on Saturday and near-impossible on Sunday
• 02NFL quarterbacks are coached to throw back-shoulder, toward the middle of the field, to buy the receiver room to get a second foot down
• 03Far more NFL plays end up under review, because the margin is inches

Which is right?

Neither, particularly. The college rule produces more completions and fewer stoppages; the NFL rule produces a higher standard of body control and more arguments. It is the same trade the two leagues make on pass interference and on the clock: college optimises for flow, the NFL for precision, and both call theirs the real version of football.