Effective interference, or the warding off of tacklers from the runner with the ball by the members of his team, is one of the absolute necessities to success in any offensive plays not directed as plunges into the opposing line. Any attempt to carry the ball which in any way develops a contest between the two forces in the open field must be supported by capable interference or it will signally fail.
The interference whereby possible tacklers are thwarted in their purpose is accomplished by the knees, body or shoulders of the interferer, the purpose being to so cast the person of the interferer between the tackier and the runner as to put the former out of the play. The portion of the interferer which can best be used for this end varies with the attitude in which the contemplative tackier is making his attempt to get at the runner. If the tackier is coming low he can be warded off by the interferer's knees; if coming in the medium position he can be checked with the hips; if still higher up, he can be met with the shoulder.
In every case the interferer must aim to meet the tackier with all his might and must prevent the latter at all events from forcing him back into the path of the runner with the ball. If he fails in this he is merely an impediment, instead of an assistance to the progress of the ball. When an in-terferer and a tackier meet, it is one or the other that is going to be put out of the play, and the interferer should see to it that the opponent is brushed aside and the path of the runner cleared of the man whom it is his duty to take care of.
An interferer should always aim to do his work intelligently. He should not wait for the man he is assigned to watch but should anticipate the rush of the opponent. He should never brush by the man but should charge him energetically, to prevent his slipping behind and dragging down the runner. The interferer must see his man and keep him in sight all the time till he is put out of the play.
Out in the open an interferer can frequently save his man from being tackled by a long dive, if it is impossible to reach him in any other way. This form of assistance to the man with the ball is often very effective.