Watch Bobby regularly hit the ball (7)
I believe the answer is:
observe
'watch' is the definition.
(observing is a kind of watching)
'bobby regularly hit the ball' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'hit the ball' becomes 'serve' (I can't justify this - if you can you should believe this answer much more).
The alternating letters of 'bobby' are 'ob'.
'ob'+'serve'='OBSERVE'
Can you help me to learn more?
(Other definitions for observe that I've seen before include "Espy" , "taking notice" , "Notice; study" , "Verbose (anag.)" , "Keep - watch" .)