Thuram scored the second to put Union Berlin 2-0 up just before the end of the first half.
Florian Neuhaus gave the home side the lead as they continued their charge towards a Champions League place finish after the Bundesliga restart.
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Thuram's celebration is almost certainly related to protests which have emerged in America as a result of the death of George Floyd after he was restrained by a police officer, who has since been charged over his death.
As well as widespread unrest across America, there were demonstrations across the world including in Britain and Canada.
Taking a knee became a widespread symbol of protest in response to police brutality against minorities when NFL star Colin Kaepernick started assuming the position during the national anthem.
Thuram is named after Jamaican activist Marcus Garvey, and his father Lilian Thuram is a well-known human rights campaigner, as well as a former international football for France.
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