The simple way:  Look for the USA Baseball sticker above the grip.

The technical specs:  It shall not be more than 33 inches in length; nor more than 2⅝ inches in diameter, and if wood, not less than fifteen-sixteenths (15/16) inches in diameter (7/8 inch for bats less than 30″) at its smallest part. Wood bats taped or fitted with a sleeve may not exceed sixteen (16) inches from the small end.

Maximum pitches per game is 75.

Additional pitch count rules can be found on our league Pitch Count page including when a putcher can be a catcher and how to figure the pitch count with the last batter.