Ride the waves (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ride the waves</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for surf that I've seen before include "Seashore foam" , "Waves breaking on the shore" , "Use the Internet" , "Breaking sea" , "White foam of breaking waves" .)