That Cuban souvenir sheet commemorates the 2nd Cuban Sports Olympiad, held in April of 2004.
The games concluded with a giant simultaneous chess match between Karpov and thousands of opponents. That is the reason why you see chess on that stamp. Of course, the stamp pictures Castro, not Karpov. Authority has its privileges.
At that time I believe it set a new world record for greatest number of simultaneous chess matches by one player. I do not know what is the current record.
The cancel on the souvenir sheet represents the final day of the Olympiad (Apr 30, 2004).

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