Box office for people’s sporting event (4,4)
I believe the answer is:
boat race
'sporting event' is the definition.
(I've seen this before)
'box office for people's' is the wordplay.
'box office' becomes 'boat' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'for' says to put letters next to each other.
'people' becomes 'race' (people can mean a national group or race).
'boat'+'race'='BOAT-RACE'
Can you help me to learn more?
(Other definitions for boat race that I've seen before include "Contest on the Thames" , "gig?" , "sporting event" , "Cockney has to face" , "Sports event" .)