Bridge players perhaps unpleasant creatures when losing the lead (5)

I believe the answer is:

easts

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'bridge players' is the definition.
Although both the answer and definition are plural nouns, I cannot understand how one could define the other.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for easts that I've seen before include "Turns to one point" , "goes to one point" .)

I've seen this clue in The Telegraph.

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