Some had a tumble and that's a fact (5)
I believe the answer is:
datum
'that's a fact' is the definition.
(singular form of 'data')
'some had a tumble' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'DATUM' is hidden within 'had a tumble'.
'and' is the link.
(Other definitions for datum that I've seen before include "Something given" , "Bit of dope" , "Given piece of information" , "Given fact" , "One item of information" .)