Although later analysis showed that the move was only sufficient for equality if Black responded correctly, Fischer did not.
Black can respond with 6...e6, when after 7.
Since White's third move carries no immediate threat, Black can respond in a wide variety of ways.
Black cannot respond by checking the white king with his queen in an attempt to escape mate.
Blacks responded by the hundreds to Dunmore's offer.
Black responded to the allegation by temporarily suspending his campaign and ordering an investigation.
Black would respond to either 24.
Blacks responded violently when the police refused to take action.
Bc4 is rare, to which Black may respond with 2...b6 or 2...d5.
Black may also respond to 3.