From Bulbapedia, the community-driven Pokémon encyclopedia.

The Sinnoh Double Battle Tournament is the tournament that Ash, Brock and Dawn took part in Tag! We're It!, Glory Blaze, and Smells Like Team Spirit. It is hosted by Enta. Its prizes are one Soothe Bell for each of the winners.

Trainers who have participated in the Sinnoh Double Battle Tournament

The following trainers have competed in the Sinnoh Double Battle Tournament:

• Ash Ketchum with Paul (Winners)
• Dawn with Conway (Runner-up)
• Brock with Holly (3rd place)
• A Psychic with a Black Belt
• Many Other trainers

Trivia

• The tournament in the anime is likely a reference to the many double battles there are on Routes 209 and 210 in Pokémon Diamond and Pearl, as it takes place in Hearthome City, which is just west of Route 209.