Schilling-Kostic gambit

I have begun to see the following response to the Italian game: 1. E4 e5 2. Nf3 Nf6 3. Bc4 Nd4

I had never seen it before, but starting somewhere in May 2019, and now, almost every time I play e4 nf3 bc4 I get this response, and I just wonder where it came from, how to beat it, and just more information about the idea. Also, the computer things Nd4 is a bad move, so how high up in the rating ladder is this played?

Hi @rajma420

Personally I don't remember ever seeing this played in response to 3. Bc4

If you check the opening explorer it seems that 4. Nxd4 exd4 5. O-O gives White a great position

I'm a newbie, I do not understand how do you get to 3 ... Nd4

1. e4 e5 2. Nf3 Nf6 3. Bc4

may be
1. e4 e5 2. Nf3 Nc6 3. Bc4 Nd4

It is just a cheap trap.
1 e4 e5 2 Nf3 Nc6 3 Bc4 Nd4?! 4 Nxe5? Qg5!
If white just avoids this: 4 Nxd4, 4 O-O, 4 c3 then white is better as black loses the tempo.