And to threaten a queen-rook fork

NG5 to put pressure on the F pawn, right?

its a good opening

The Variation below may be a good defense of the combination proposed by texasaboy

for this black can play Traxler gambit and destroy white

the correct move after 4.Ng5 is ...d5. after that:

5.exd5    ....    b5!

if 6.Bxb5 then ... black plays Qxd5(attacking the bishop and the pawn at g2)

if 6.Bb3 or Be2 then ...black plays Nd4

if 6.Bd3... well that's bad enough.

it's better for black after ...5. b5!

white's best move is 6.Bc1(saving the g2 in advance so that Qxd5 causes no threat)

after which black should play Nxd5 and then white should play Bxb5 but black can save the knight by Bb7(not Bd7 as it causes inconvenience for king side attack and the bishop has more scope in b7 after the knight moves than in d7) it took me a long time to write this explanation

7. N3d4#

BecareFull A trap for White!!

5. exd5   Nd4

6. e6      Qxd6

7. Nxf7     Qc6

8. Nxh8   Qxg2

9. Rf1      Qxe4 +-

(9. Rg1   Qxg1+)

10. Be2    Nf3++

@wubowen100

6.Qf3 f6 7.Qh5+ g6

The reason for white's knight going to g5 is not only to defend its pawn on e4 but to also create a devastating fork by attacking black's pawn at f7 and being guarded by white's bishop at c4, had black not defended at d5. 

Hello. I'm a newbie. Can someone tell me why white would want to go 4. Ng5? Wouldn't 4. Nc3 or 4. d3 be better ways of defending the e4 pawn?

What is the reason for 4. Ng5?  I see that it is defending e4, but it is now hanging. 

This attack always messes me up, I hate draggin my King out into the battlefield.

Ahh, the good ol' fried liver.