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Gym sample I adulterated with 50% of coke, in major sporting event (7,5)

Ross

I believe the answer is:

olympic games

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

'major sporting event' is the definition.
'olympic games' can be an answer for 'event' (Olympic Games is an example). I am unsure of the 'major sporting' bit.

'gym sample i adulterated with 50% of coke' is the wordplay.
'adulterated with' indicates anagramming the letters (I've seen this in other clues).
'50% of' suggests halving the letters.
'coke' halved is 'co'.
'gym'+'sample'+'i'='gymsamplei'
'gymsamplei' mixed up with 'co' makes 'OLYMPIC GAMES'.

'in' acts as a link.

Can you help me to learn more?

(Other definitions for olympic games that I've seen before include "International athletic event" , "Event whose sign here" , "sporting festival" , "Two thousand and twelve London event" , "Four-yearly event" .)

I've seen this clue in The Telegraph.
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