1. To compete against someone or something (in some sport, game, or competitive activity). I hate playing against my dad in chess—he always beats me! The last time we played against our cross-town rivals we lost by just one point, so we're looking for revenge this year. I wish my friends liked to play video games so I wouldn't have to always play against the computer.
2. To engage in some sport, game, or other competitive activity against another person or thing. In this usage, a noun or pronoun is used He was such a star athlete that he was playing soccer against high schoolers when he was just 13. I always lose when I play chess against the computer. I would love to play video games against my boyfriend, but he has absolutely no interest in them.
3. To manipulate two or more people such that they dispute or conflict with one another in a way that is to one's benefit or advantage. He played the board members against each other so that he could steal the company's money without them noticing. Janet has been playing Mary against her boyfriend, Mike, so that they'll break up and Janet can date him herself. Don't you see? Tom's been playing the boss against me so that he'll have a better shot at the promotion.
play someone against (someone else)
to cause someone to dispute with someone else. Don tried to play George against David, but they figured out what he was up to. Alice never managed to play Tom against Fred.
play against someone or something
to compete against someone or something in a team sport. We won't be ready to play against the other team this weekend. We refuse to play against you until the field is in better condition.