Guinness head on a number of beers from the bar arena (6)
I believe the answer is:
Here is my best explanation:
'arena' is the definition.
'guinness head on a number of beers from the bar' is the subsidiary indication.
'head' indicates taking the first letters.
'on' is a charade indicator (letters next to each other).
'a number of beers from the bar' becomes 'round' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'guinness' is 'g'.
(Other definitions for ground that I've seen before include "Land surface", "Reduced to powder", "Foundation", "Stop (a pilot) flying", "Earth; stop from flying", "Pulverised; land", "Powdered; land", "Bring down", "The solid surface of the Earth" and "cause".)