Knothole rule on bats:

Approved baseball bats are any unaltered commercially manufactured bats
available for retail purchase with the following exceptions:
(a) per official baseball rule 1.10 (a) max. diameter of the bat barrel is 2 and 3/4 inches

(b) softball bats are not allowed to be used

(c) Composite material and flex handle bats are prohibited unless the are "bpf" rated, team managers are responsible for assuring all bats used by their team are "bpf" rated

(d) For players in A-Jr/14U and up, the maximum difference between bat length and bat weight is minus three (-3)

Penalty: Player is out and the ball is dead immediately and the bat is immediately removed from the game and the bench are.