Problem Collisions with small objects

Hi all !!

I have a problem with my game, and I do not really know how to solve it. I am developing a football 3D game where the football players are kids. So far I have already developed the game with all the AI and so on.

But my problem is that if any player has the ball and an enemy makes a frontal collision, the enemy jumps a lot !! I think the problem comes because of the size of the objects (players are 3.5 y-axis, whereas the ball is only 0.5) Because If I have the same collision without the ball anything happens

I would like to remove this behaviour because it is quite strange that some players do huge jumps due to collision.

Do you know how can I solve it?

Thank you very much