Chess Opening Theory/1. e4/1...e5/2. f4/2...exf4/3. Nf3/3...d6

=Fischer Defense= Fischer called 3... d6 "a high-class waiting move." The idea of it is to avoid the Kieseritzky Gambit (1.e4 e5 2.f4 exf4 3.Nf3 g5 4.h4 g4 5.Ne5) and free the queen's bishop, as well as giving an extra space for the king to run to if necessary, while also taking away the e5 square from the f3 knight, potentially trapping it. However, it also blocks the f8-bishop.

Theory table
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1.e4 e5 2.f4 exf4 3. Nf3 d6