Define momentum in terms of football.

Think of Einstein’s theory of general relativity. If a wide receiver making a catch collides in midair with the defender, the defenders often fair little better in these situations because they tend to run a little larger than receivers. But it is not a matter of force. Newton’s third law of motion ("to every action there is an equal and opposite reaction / the mutual actions of two bodies upon eachother are always equal and directed to contrary parts") implies that this issue has to do with momentum, the product of mass and velocity. A force between two objects is an interaction that changes momentum. If the momentum of one increases, the momentum of the other will decrease by a substantial amount. All that is needed to be thought about is is the momentum right before the two come into contact and the momentum right after they stop interacting.