Bag some winners at Cheltenham (7)
I believe the answer is:
'bag' is the definition.
(satchel is a type of bag)
'some winners at cheltenham' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'SATCHEL' can be found hidden inside 'winners at cheltenham'.
(Other definitions for satchel that I've seen before include "Bag for school books" , "Shoulder bag as for schoolbooks" , "Schoolbag found in chalets" , "Text mark for an insertion" , "Bag with a strap for books" .)