Beam-on

Wave direction and frequency (period) are two factors that influence the effect of waves on a moored ship. Whether the ship responds by surging, swaying or yawing will depend on whether the waves are striking the moored vessel head-on, beam-on or quartering, the frequency of the waves and the manner in which the tanker is moored.

Source: wiktionary

"The jetski slewed around and hit the buoy beam-on. A bystander on the dock hastily threw a lifeline, which flew over the swimming jetskier's head and hit our boat beam-on, tangling itself in the shrouds."

Source: wiktionary