Having played this game for 35 years, it is rare that I see something that I have never seen before. But this one in a BBO ACBL matchpoint game was new to me.
My RHO held this hand in second seat. It might take you some time before you come up with the call that he found.
1♦.
It is usually a good thing when your partner has 5 card support for your overcall. Not this time. The opps wound up in 5♦x going for 500 (it could have been 800) at equal nonvul when partner tabled xxx Jxxx KJ98x J.
Needless to say, I was impressed.

Help

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ing) tr. v. - Any bid made by bridge player with which partner disagrees.
(1♣) - ?