Comedian Tommy had to play ball (9)
I believe the answer is:
cooperate
'play ball' is the definition.
(I've seen this before)
'comedian tommy had' is the wordplay.
'comedian tommy' becomes 'cooper' (I can't explain this - if you can you should give a lot more credence to this answer).
'had' becomes 'ate' (e.g. I had an ice cream).
'cooper'+'ate'='COOPERATE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for cooperate that I've seen before include "getting act together" , "work hand in glove" , "Play ball with" , "Work together on a common enterprise" , "Work constructively with others" .)