Hello I am new to physics and I tried and tried to answer this question but I can't understand it. Can someone please help me solve it?

When a Football Defensive lineman wants to stop an opponent, he puts his shoulder into his opponent's body and lifts up. How does this affect the ability of his opponent to accelerate?

anyone please

The key to this situation is 'How does he apply force backwards so that he is accelerated forwards?' - and the answer is that he drives his studs into the ground and pushes down with his legs, if his legs are no longer in contact with the ground, or have lost some of their purchase, then he can no longer give himself the thrust.
This is concerned with the Newtonian idea that each action has an equal and opposite reaction and is typified by the equation F=ma. The players force against the ground causes his mass to be accelerated in an opposite direction.

thank you very much