Possible Clues:

• Still on board for this game?
• Aboard ship there's still a cut-down version of ball game
• Each of them is odd, but in the middle, not
• Rugby game; card game
• Some naturals
• Nothing odd in having such a number in the ship
• Common craps rolls
• Singular odds for rugby competition
• See 15
• Robert Plant: "Sixes and ___"