They placed a couple of sticks in the sand to mark the goal.
There are probably not many beaches with such a gradual slope that there is enough room to set up a soccer game on the beach. This photo was taken near low tide at the southern end of Tamarindo beach, looking out towards San Francisco point. At this same spot during high tide in a few hours, this group might try to play a beach version of water polo in this location.
We are showing photos of Hawaii this week on our Viva la Voyage travel photo site.