This seems like a rather shellfish thing to do. According to Polygon,
[Juan] DeBiedma, a longtime Super Smash Bros. Melee pro who represents esports organization Team Liquid, was playing in the grand finals of Pound 2019 against Cloud9’s Joseph “Mango” Marquez after avoiding elimination and making a tense run through the losers bracket. DeBiedma claimed the grand finals, and then an angry fan threw the dead crab he had smuggled into the venue.
. . .
The organizers of Pound have announced that they intend to permaban the crab thrower from future tournaments, and his name will also be distributed to other tournament organizers. Pound’s staff said they do not intend to release the fan’s name publicly.