From's Gambit, Lasker Variation

The Lasker Variation is the most combative of Black's fourth-move options in From's Gambit. With 4...g5 Black aims for ...g4, expelling the knight from f3 so that ...Qh4+ and a sacrifice on g3 become available against the exposed king. Emanuel Lasker first employed it against Henry Bird at Newcastle upon Tyne in 1892. The price is a further loosening of Black's own kingside on top of the pawn already invested, and IM Timothy Taylor rates the line as dubious.

White has two principal answers. The sharper 5. g3, chosen in about half of the games, blunts the diagonal in advance and meets 5...g4 with 6. Nh4; Taylor judges White to be clearly better there, though the play stays highly tactical. The quieter 5. d4 g4 6. Ne5 Bxe5 7. dxe5 Qxd1+ 8. Kxd1 removes the queens at once and leaves White a modest but lasting edge, while 6. Ng5 instead involves a dubious piece sacrifice. In online play 5. d4 has produced White's best results, and the engine gives White a slight advantage overall.