My Logic - please try and break it

[Martin_Salter]

private int bowl = 0;

public Action Bowl(int pins)
{
    if (pins < 0 || pins > 10) { throw new UnityException("Invalid Pin Count"); }
    bowl++;
    bowls[bowl - 1] = pins;

    switch (bowl)
    {
        // FRAME 10
        case 19:
            if (pins == 10) return Action.Reset; // strike in bowl 19
            return Action.Tidy;
        case 20:
            if (bowls[19 - 1] == 10 && pins < 10) return Action.Tidy; // Open 20 after strike in 19
            if (pins == 10 || pins + bowls[19 - 1] == 10) return Action.Reset; // Strike or spare in bowl 20
            return Action.EndGame;
        case 21:
            return Action.EndGame; // Definitely no more after bowl 21
        default:
        // FRAMES 1 To 9
            if (bowl % 2 == 0) return Action.EndTurn;  // Second bowl of frame 1-9 always ends turn
            else if (pins != 10) return Action.Tidy;  // First bowl of frame 1-9 is open
            else // First bowl of frame 1-9 is Strike
            {
                bowls[bowl] = 0;  // Mark next roll as zero
                bowl++; // Skip next roll
                return Action.EndTurn;
            }
    }
}