Flab lost exercising in US game? (8)

I believe the answer is:

softball

I'm a little stuck... Click here to teach me more about this clue!

'us game?' is the definition.
'softball' can be an answer for 'game?' (softball game is a kind of game). I'm not certain of the 'us' bit.

'flab lost exercising' is the wordplay.
'exercising' indicates an anagram.
'flab'+'lost'='flablost'
'flablost' is an anagram of 'SOFTBALL'.

'in' is the link.

Can you help me to learn more?

(Other definitions for softball that I've seen before include "sport!"" , "game" , "played by young American" , "Junior variant of baseball" .)

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