Blitz Concentration!

My grandson almost invented an exciting new game. I'm helping out now, to realize the full potential of his idea. I'm sure you already own the necessary equipment to play this game, and I recommend it to you.
"Concentration" is a game with a deck of cards or objects that are paired on one side, but all the same on the other side. The items are distributed randomly on a surface and you take turns turning over two cards to find matching pairs. Unmatched cards are turned face down again, but if you remember what and where they are, better than your opponents, you'll probably win.

Concentration comes in many, many forms. My grandson asked me to play some game with him, and I quickly realized he had a sort of concentration deck. I checked the rules of the game with my son, who confirmed we were indeed about to play Concentration, but he added, vaguely, "There's also another rule. Sometimes you're not allowed to play the card you want."
That made no sense to me so I ignored him and started the game. After awhile I saw my chance; a mismatched card would match a card previously turned, and I remembered where it was. As I reached for that other card, my grandson said, "You're not allowed to play that card now."
Obligingly I turned over some other card, and my grandson got the pair instead. And, I then understood the "other" rule my son had been explaining.

Now instead of calling my grandson a sneaky cheat - let's avoid the blame game - I want to move forward into the exciting new world he's created. Here are the changed rules you need to play: Blitz Concentration!
When it is any player's turn to play, he or she turns over one card, and then uses the same hand to turn over a second card. But if any other player places a hand on another card first, he may not turn that card over at this time. The other players may each block at most one other card in this way. Quickness of hand and thought are what count, in Blitz Concentration. (I suspect this game will be best with just two players. Too many players, too much defense.)

Backyard tomatoes harvested so far: Cherry, 3. Plum, 0. Big Girl, 0.