The headword is aorist infinitive of ῥαπίζω , a verb related to the noun ῥαπίς , genitive ῥαπίδος : see rho 46 and the cross-references there. (In context the verb may, but certainly does not have to, imply striking with such a stick.)
Same entry in Photius, similar ones elsewhere. The headword is evidently quoted from somewhere -- perhaps Plutarch, Alcibiades 16.5 (where the over-competitive A. does this to Taureas, a rival choregos).