Problem over contact sport (4)

I believe the answer is:

sumo

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'contact sport' is the definition.
'sumo' can be an answer for 'sport' (I've seen this before). I am unsure of the 'contact' bit.

'problem over' is the wordplay.
'problem' becomes 'sum' (as in a mathematical problem).
'over' becomes 'o' (cricket abbreviation).
'sum'+'o'='SUMO'

Can you help me to learn more?

(Other definitions for sumo that I've seen before include "Japanese form of wrestling" , "Large Japanese wrestler" , "Jap. wrestling" , "foreign form of fighting" , "Type of Japanese wrestling" .)

I've seen this clue in The Independent.

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