Impulse is the product of the applied force and the time over which that force is applied.
Because impulse is a product like momentum, the same impulse can be applied if one varies either the force of impact or the time of contact. For the discussion, we will consider an elastic collision , in which the players do not remain in contact after they collide. If the ball carrier and tackler have equal momentum, the forward momentum of the ball carrier is exactly matched by the backward momentum of the tackler. The motion of the two will stop at the point of contact. If the ball carrier has more momentum than the tackler, he will knock the tackler back with a momentum that is equal to the difference between the two players, and will likely break the tackle.