Such sports are no fun for some participants (5)

I believe the answer is:

blood

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'such sports are' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for blood that I've seen before include "Gore" , "Red fluid" , "It contains plasma and platelets" , "Vein filler" , "It's said to be thicker than water" .)

I've seen this clue in the Evening Standard.

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