A dog behind the ball can be referred to as "a dog that is behind the ball." The phrase comes from a scenario in which the ball is in front of the dog, and the dog is positioned behind it.

Here are some example sentences using this phrase:

The dog was behind the ball, eagerly waiting to chase after it.
The child threw the ball, and the dog ran to get it, but it ended up behind the ball.
The dog's position behind the ball made it difficult for him to catch it.

Example sentence translations:

小狗渴望地站在球的后面等待追逐。
孩子扔了球，小狗跑去抓，但最终在球的后面。
小狗站在球后面的位置使得它很难抓住球。