"Playing hard ball" is a commonly used phrase that means to be uncompromising and aggressive in negotiations or disputes. However, there are several synonyms that can be used instead of "playing hard ball" to convey a similar meaning. Some of these synonyms include "being tough," "being firm," "being unyielding," "being inflexible," and "being resolute." These words suggest a strong and determined approach, indicating that one is not willing to compromise easily or back down from a challenge. Whether you're negotiating a business deal or trying to resolve a conflict, using these synonyms can help convey your message effectively and assertively.