The term "in fits" can be used to describe a range of behaviors or actions that are sudden and erratic. Synonyms that can be used in place of this phrase include "spasmodic," "paroxysmal," "convulsive," "twitchy," "jerky," "unpredictable," and "intermittent." Each of these words conveys a sense of irregularity or impulsivity that is often associated with behaviors that occur "in fits." By using synonyms in place of the same word, you can vary your language and create a more descriptive and engaging writing style.