They were not permitted to play ball or climb trees.

VOA: special.2010.05.26

I just want to exercise or something I'll go and play soccer, basketball, dodge ball, things like that.

我想锻炼的时候我就去踢足球、打篮球、打躲避球，这一类的。

我喜欢运动 - SpeakingMax英语口语达人

So,their reward for finding a scat is they get to play ball for two to three minutes and that keeps them good all day long."

VOA: standard.2010.02.22

Perhaps they did this after expressing hope that they could play ball with each other,meaning that they could learn to cooperate.

VOA: special.2010.08.22

"And,we come and check it out. And,all of our dogs are extremely ball driven they love to play.

VOA: standard.2010.02.22