1
general::
Phrase(s): play into someone’s hands
Fig. [for a person one is scheming against] to assist one in one’s scheming without realizing it. • John is doing exactly what I hoped he would. He’s playing into my hands. • John played into my hands by taking the cash he found in my desk. I caught him and had him arrested.
McGrawhill's American Idioms And Phrasal Verbs