Il l’a laissé sur le carreau = He killed him (or, left him for dead on the ground).
Il est resté sur le carreau = He was killed on the spot, left for dead on the ground.
[Formerly the floors of rooms were paved with square tiles or bricks called carreaux. Kitchens are still so paved in France, and often ground-floor rooms in the country.]
Carte
Battre les cartes = To shuffle the cards.
Donner les cartes = To deal the cards.
Brouiller les caries = (fig.) To sow discord.
Elle lui a tiré les cartes = She told his fortune (by cards).
Il a vu le dessous des cartes = He has been behind the scenes; he is in the secret, “in the know.”
Jouer cartes sur table = To play openly; To act frankly.