Depends what you consider ab work.
If its crunches and the like, you're mainly wasting your time.
Med ball work can be done quite often, even 6-7 days per week. 2-3 of those sessions should be ballisic and high effort, while the others should be for recovery, proper movement patterns and range of motion improvement. The med ball is eaisly the most under-used tool by athletes, especially baseball players.
True core work should be done 2-3 times a week as well.