The word "hammiest" refers to an exaggerated or theatrical way of performing, particularly in acting. Its antonyms would therefore be words that convey the opposite meaning, such as "subtle," "understated," "quiet," "restrained," "realistic," and "naturalistic." These words suggest a performance that is more nuanced and authentic, with a focus on subtlety and realism, rather than dramatic flourishes and overacting. While there is certainly a place for hammy performances in certain contexts, particularly in comedy or satire, a more subdued and nuanced approach is often preferable for more serious or emotionally complex roles.