Chess Opening Theory/1. e4/1...e5/2. Nc3/2...Bc5

Anderssen Defence
This move allows White to immediately go after the bishop with 3. Na4?!, but that allows Black to take advantage of the undefended a4-knight using the Hamppe-Meitner sacrifice 3...Bxf2+!, named after the Immortal Draw (Hamppe-Meitner, Vienna 1872) Kxf2 Qh4+. It is premature to derail the knight on the rim like this when Black doesn't have any other piece out.

The game continued: Kxf2 Qh4+ Ke3 Qf4+ Kd3 d5 Kc3 Qxe4 Kb3 Na6 a3 Qxa4+!! Kxa4 Nc5+ Kb4 a5+! Kxc5 Ne7 Bb5+ Kd8 Bc6 b6+ Kb5 Nxc6 Kxc6 Bb7+ Kb5 Ba6+ Kc6 Bb7+. 1/2-1/2.

The simple 3. Nf3 gives White a slight advantage, though.

Theory table
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1. e4 e5 2. Nc3 Bc5