Was judge free to frolic in grass? (8)

I believe the answer is:

refereed

'was judge' is the definition.
(was a referee)

'free to frolic in grass?' is the wordplay.
'to frolic' indicates an anagram.
'in' indicates putting letters inside.
'grass?' becomes 'reed' (type of grass plant).
'free' is an anagram of 'efer'.
'efer' placed inside 'reed' is 'REFEREED'.

(Another definition for refereed that I've seen is " Acted as umpire".)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app