Book about Hearts initially exaggerated their goal tally (10)
I believe the answer is:
scoresheet
'initially exaggerated their goal tally' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'book about hearts' is the wordplay.
'book' becomes 'sheet' (I can't justify this - if you can you should believe this answer much more).
'about' is an insertion indicator.
'hearts' becomes 'cores' (core can mean the heart of something).
'sheet' enclosing 'cores' is 'SCORESHEET'.
Can you help me to learn more?
(Other definitions for scoresheet that I've seen before include "goal to get on this?" , "Record of players' performances" .)