Bag some prizes at Chelsea (7)
I believe the answer is:
satchel
'bag' is the definition.
(satchel is a type of bag)
'some prizes at chelsea' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'SATCHEL' can be found hidden inside 'prizes at chelsea'.
(Other definitions for satchel that I've seen before include "What's carried by pupils" , "Text mark for an insertion" , "Schoolbag found in chalets" , "Bag with a strap for books" , "Bag -- latches (anag)" .)