Answer:
The normal force that the wall exerts on the ball.
Step-by-step explanation:
Erica throws a tennis ball against a wall, and it bounces back. Here Newton's third law of motion follows. When the ball hits the wall, the wall will also exert an equal and opposite force on the ball as per third law. The opposite force that wall exert on ball is normal force which is responsible for sending the ball back to Erica.
Hence, the force is normal force exerted by the wall on the ball.