There are plenty of synonyms that can be used for the phrase "play dirty". They all have a common theme of being unethical or unfair. Some possible synonyms include: cheat, deceive, manipulate, betray, hoodwink, swindle, trick, con, mislead, or outmaneuver. These words all convey a sense of someone trying to take advantage of others through dishonest means. It's important to note that playing dirty is not an admirable trait and can often lead to negative consequences. It's always important to approach situations with honesty and integrity, even if it may not always be the easiest or most convenient option.