Take part for a particular reason, as in We're not playing for money, just for fun. A special usage of this idiom is play for laughs, that is, with the aim of arousing laughter.
play someone for. Manage someone for one's own ends, make a fool of, dupe or cheat. For example, I resent your playing me for a fool, or He suddenly found out she'd been playing him for a sucker. This usage employs play in the sense of "exhaust a hooked fish," that is, manage it on the line so that it exhausts itself. [Mid-1600s]