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'm not certain of the 'contact' bit.

'problem over' is the wordplay.
'problem' becomes 'sum' (arithmetic 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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