Dan's running on the beach (4)
I believe the answer is:
sand
'the beach' is the definition.
'dan's running' is the wordplay.
'running' indicates anagramming the letters (the letters run around to different places).
'dans' with letters rearranged gives 'SAND'.
'on' acts as a link.
(Other definitions for sand that I've seen before include "Beach grit" , "Beach constituent" , "Very fine grains of rock, as on beach" , "lover of Chopin" , "Grains by the sea" .)