But what if they take no damage or they do more damage than they took does that mean the fleet selected gets the rubies?

No whoever does the most damage to that fleet wins.

But it can't be damage from that fleet attacking you and crushing your fleet.
Like say Perses is the "Fleet of the Day" and he gets attacked by 3 people and he himself attacks 2 others.
The 3 people that attack him each do 1-5 million TD to his fleet. (hypothetical situation )
And the 2 people that Perses attacks lose their whole fleets but do 10 million TD in that combat.
Those 2 people would not be in the contest because they got attacked and did not Ninja.
The prize would go to one of the 3 attackers unless one of the people that got attacked ninja'd Perses and at least gets a tie.

Another and/or option would be "Hit of the week" to award the largest hit of the week.
I don't know about rubies on this one though maybe just a medal or else Perses will win this one every week lol


EDIT* And to answer your question... lol
If the fleet of the day takes no damage, nobody wins.
And whoever does the most damage, if this fleet does more damage then it recieves it goes back to who has done the most to this fleet.
You cant damage your own fleet.
If this fleet takes no damage can have a survivalist award for surviving the hunt.