Contested Game Ball is a uncommon Artifact card from The Lost Caverns of Ixalan (LCI), collector number 251. Current market price: $0.20 (foil $0.29), TCGplayer market prices via Scryfall.
Whenever you're dealt combat damage, the attacking player gains control of this artifact and untaps it. {2}, {T}: Draw a card and put a point counter on this artifact. Then if it has five or more point counters on it, sacrifice it and create a Treasure token.