The phrase "had a whack" is often used to refer to an attempt or effort to do something, often unsuccessfully. The antonyms for this phrase would be "succeeded," "nailed it," "accomplished," or "ace it." These words imply that the individual was able to accomplish their task, and that their efforts were met with success or satisfaction. Other antonyms could include "gave up," "failed," or "struggled." These words would suggest that the individual was unable to complete their task, either due to external factors or personal limitations. With the right mindset and perseverance, success can be achieved, and the phrase "had a whack" can be replaced with more positive language.