Follow tennis rules regularly (5)
I believe the answer is:
ensue
'follow' is the definition.
(thesaurus)
'tennis rules regularly' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'tennis'+'rules'='tennisrules'
The alternating letters of 'tennisrules' are 'ENSUE'.
(Other definitions for ensue that I've seen before include "Come to pass" , "Follow subsequently" , "Occur afterwards" , "Follow afterwards" , "Turn out" .)