Why is tripping illegal in the NFL?

Tripping became a hot topic of debate after Green Bay Packers safety Adrian Amos tripped San Francisco 49ers quarterback Jimmy Garoppolo.

Many fans were confused by the whole thing: that in a league as physical as the NFL, something as simple as tripping is outlawed. But the question comes to be, how did it come to be like this? Why is smashing into a player and making them stumble alright, but not tripping?

The answer lies in the history of the game itself and how Gridiron football, encompassing American and Canadian Football, arose from the wider footballing codes.

American Football and its laws on tripping

Most fans who comment on tripping seem to believe it has been outlawed because of the potential injuries it can cause. But that doesn't quite add up because tackles that cause opposition players to topple over are allowed.

In fact, the tripping rule dates back all the way to the origin of football itself. Football has various codes out of which American football is one. Soccer or association football is another, and rugby football, encompassing both rugby union and rugby league, is another separate form. Tripping is foul play in all of these codes.

The evolution of American football from rugby football happened when Walter Camp proposed that scrummaging be replaced by a clean line of scrimmage. In rugby union, once the ball is put down after being fairly held, it becomes contested and can lead to a turnover. In football, the line of scrimmage is clean and contests only begin after the snap.

Rugby football itself arose as a version of football in Rugby School, a boarding school in the United Kingdom. Legend has it that it arose when a pupil named William Webb Ellis picked up the football and ran.

Which brings us back to football before rugby. There was a time when hacking and tripping were allowed but outlawed not only because of the danger but because it interfered in playing the game of football i.e. playing the ball with the foot.

Even today, with the exception of the forward pass, all other plays that advance a team towards the opposition endzone such as field goals, kicks and punts are played with the foot and hand passes can only be lateral. To allow for the possibility of this to occur unhindered, the outlawing of tripping exists as a vestige in the NFL as well.