Season 1

Season 1 of GO Battle League lasts from March, 2020 to May , 2020. It is preceded by Preseason.

Formats

 * Battle League Great.png Great League: March, 2020 to March , 2020
 * Battle League Ultra.png Ultra League: March, 2020 to April , 2020
 * Battle League Master.png Master League: April, 2020 to April , 2020
 * GO Battle League.png All three Leagues: April, 2020 to May , 2020

Ranks and Ratings
The requirements are different from Preseason.

Rewards
Basic Premium

The random items include:
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Reaching rank 10 can earn avatar items and an avatar pose inspired by Steven.

Pokémon
Metagross is the first guaranteed encounter. Pikachu Libre is the first encounter in rank 10, one only.

Certain Legendary Pokémon or Mythical Pokémon can be obtained starting at rank 4 during their time in tier 5 Raid Battle.

End-of-season rewards

 * (rank 7 or above)

Events

 * GO Battle League Season 1 Launch Celebration was held to promote Season 1.
 * When Season 1 was initiated, the rank and rating of Trainers were slightly altered from that in Preseason. Later, Niantic adjusted all Trainers to rank 1. If a Trainer claimed the end-of-preseason rewards during this time slot, their Preseason record would be lost.
 * Due to coronavirus outbreak, trainers do not require walking or PokéCoins to unlock battle sets since the start of Season 1 to April.

Maintenance

 * March, 2020 - soon after the start of Season 1, GO Battle League was closed for 20 minutes to adjust rank and rating
 * On the same day, it was down for 3 to 5 hours again.
 * March, 2020 - temporarily closed for 1 to 3 hours