I've always seen that as a repetitive, aggressive, action myself. Not a single strike but the full iterative function of the imperfect. Lifting, slamming, men screaming and trying to avoid violence even as Polyphemos breaks them etc.
I don't know if there's an attempt to tone down Homer, mayhap it just makes better English.
Will not answer questions which only need a basic knowledge of grammar. Pay attention to the textbook.