The Collaborative International Dictionary of English v.0.48:

Larrup \Lar"rup\, v. t. [imp. & p. p. Larruped; p. pr. & vb.
   n. Larruping.] [Perh, a corrupt. of lee rope, used by
   sailors in beating the boys; but cf. D. larpen to thresh,
   larp a whip, blow.]
   To beat or flog soundly. [Prov. Eng. & Colloq. U.S.] --Forby.
   [1913 Webster]