Swimmer regularly beat runner, say (6)
I believe the answer is:
carpet
'runner say' is the definition.
(I know that runner is a type of carpet)
'swimmer regularly beat' is the wordplay.
'swimmer' becomes 'carp' (carp is a kind of fish).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'beat' are 'et'.
'carp'+'et'='CARPET'
(Other definitions for carpet that I've seen before include "A red ...... is rolled out for VIPs" , "Floor covering of heavy fabric" , "Reprimand, rug" , "has pull up sharply" , "lecture?" .)