The top 10 companies in the sports betting industry this year (2021) are as follows:
1. Flutter Entertainment: A global leader in online sports betting and gaming, operating popular brands such as Betfair, Paddy Power, and FanDuel.
2. Entain (formerly GVC Holdings): Another major player in the industry, owning and operating well-known brands like Ladbrokes, Coral, and bwin.
3. DraftKings: A prominent US-based company that provides online sports betting and daily fantasy sports services.
4. William Hill: A long-established bookmaker with a strong presence in both online and offline sports betting markets.
5. Bet365: A leading online gambling company offering sports betting, casino games, and other gambling products.
6. 888 Holdings: A well-established global operator featuring a sportsbook, online casino, and poker room among its offerings.
7. Kindred Group: The parent company of several popular brands, including Unibet, 32Red, and Maria Casino, offering sports betting and online gaming.
8. The Stars Group: Known for its flagship brand PokerStars, the company expanded into sports betting with the acquisition of Sky Betting & Gaming.
9. Betsson AB: A Swedish gambling company operating various brands across multiple markets, including Betsson, Betsafe, and NordicBet.
10. Betway: A globally recognized brand that offers sports betting, casino games, and online poker.
Please note that rankings can vary depending on various factors, and the nature of the sports betting industry makes it susceptible to frequent changes and mergers/acquisitions.