An Etymological Dictionary of the German Language/Schlag
Schlag (1.), m., ‘sort, race, family, class’; see Geschlecht.
Schlag (2.), m., ‘stroke, blow,’ from the equiv. MidHG. slac (gen. slages), OHG. slag, m.; a verbal abstr. of the root slah, ‘to strike.’ ModHG. schlagen, ‘to strike, beat, pulsate,’ MidHG. slahen, OHG. slahan, ‘to strike’; the g of the ModHG. vb. is due to the grammatical change of h to g. Comp. Goth. slahan, OIc. slá (also ‘to mow down’), AS. sleán (from sleahan), E. to slay, Du. slaan, OSax. slahan, ‘to strike.’ Teut. root slah (slag), from pre-Teut. slā̆k; akin to Gr. λακίζω, Lat. lacerare, ‘to tear to pieces or rags,’ for slak-?. A root similar in sound appears in OIr. slechtaim, sligim, ‘I strike’ (root sleg). See Geschlecht and schlau.