Antonyms for the phrase "keeps the ball rolling" would include "stagnates," "stalls," "stagnates," "delays," "obstructs," and "impedes." All of these antonyms denote an unwillingness or inability to move forward or progress, and they suggest a lack of momentum and energy. Alternatively, some synonyms for "keeps the ball rolling" might include "drives," "propels," "pushes," and "propagates," all of which indicate a forceful and dynamic approach to maintaining momentum and making progress. Ultimately, whether we use antonyms or synonyms, the idea of keeping the ball rolling is a critical one in any context where progress and motion are important.