I tried to convince John to work on the project without letting anyone else know he was helping, but he didn’t want to play ball.

The words are an expression sometimes used when a person does not want to do what you hope that person will do.  Sometimes, that other person does not agree with you, so they will not do what you ask them to.

[我試著要約翰暗中協助該方案之進行，但他不願配合。]

本句 play ball 指的是照他人所要求的去做，也就是配合辦理的意思；通常只用在表達拒絕（或否定意味）的句子裡。