The NFL suspended Shaw indefinitely last week, with his punishment to cover at least the entirety of the 2020 season. He'll be eligible to file for reinstatement starting Feb. 15, 2021, pending the result of his appeal.
The Cardinals placed Shaw on injured reserve in August, and he has yet to play for the team in 2019.
Purdum reported Shaw was in Las Vegas on Nov. 10 and placed at least one bet on a three-team parlay that included the Cardinals' Week 10 matchup with the Tampa Bay Buccaneers. He wagered against Arizona, hoping the Buccaneers would cover the second-half spread.
The Caesars Entertainment sportsbook reached out to the Nevada Gaming Control Board and the NFL upon realizing Shaw was betting on NFL games.
NFL Network's Ian Rapoport reported Shaw is claiming to have "a misunderstanding of the Supreme Court's ruling" in 2018 that lifted the ban on sports gambling and allowed states to craft their own laws.
CNBC's Jabari Young noted the Cardinals could potentially void Shaw's one-year, $895,000 contract under the current collective bargaining agreement if the league determines he violated the "Integrity of Game" clause.
Art Schlichter in 1983 is the last NFL player to earn a gambling-related suspension.