A number of baseball organizations have their rules listed. MTS gave you the site for the pro rules. The NCAA, USSSA, and Dixie also provide theirs, free of charge:
Little League does not put its rules on their website. NFHS (high school) does not either. PONY used to, but not anymore. You can still find older versions of the PONY rules.
ACTIVE is the leader in online event registrations from 5k running races and marathons to softball leagues and local events. ACTIVE also makes it easy to learn and prepare for all the things you love to do with expert resources, training plans and fitness calculators.