Complex sentence: One cannot score a boundary six in byes--nor in leg byes, wides or no balls; a boundary six can only be scored if the ball has made contact with the bat or the hands or gloves holding it.
Split into simpler sentences: One cannot score a boundary six in leg byes--or in byes, wides or no balls. A boundary six can only be scored if the ball has made contact with the bat or the hands or gloves holding it.