The rook couldn't move, e.g. 4.Rfe1 Rxf2! 5.Kxf2 Qe3#

A strong sacrifice that will leave the enemy king in trouble on the light squares.

Seizing the long diagonal in order to enhance the attack.

Preparing a decisive discovered check.

White resigned.

Sacrificing the exchange in the fight for the initiative.

3.dxc5? Qa5+ -+

Clearing the centre before White castles away from the e-file.

4.0-0? exd4 5.Nxd4 Qb6 Black wins a piece
4.dxe5 d4 , followed by ...Nxe5
4.dxc5 d4 , followed by ...Nxc5, also favours him.

With ideas like ...c5-c4 and ...Bb7-a6 Black keeps a strong initiative.