Some sent Riesling for competitors (7)
I believe the answer is:
entries
'competitors' is the definition.
(I've seen this before)
'some sent riesling for' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'ENTRIES' is hidden within 'sent riesling for'.
(Other definitions for entries that I've seen before include "making appearances on stage" , "Items listed" , "Diary items; competitors accepted" , "Sneer it (anag.)" , "Submissions to competition" .)