Answer
The glove exerts a force on the oncoming ball, in a direction opposite to the ball's velocity, that slows it down. Newton's third law tells us that the baseball exerts an equal and opposite force on the glove.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.