Can a player use Sprite Call to play a sprite token directly to an uncontested battlefield when an opponent moves into it, triggering a showdown?

Ruling: No. While moving into an uncontested battlefield does start a showdown and players can play actions during showdowns, tokens and units can only be played at your base or battlefields you control. Since the opponent doesn't control the battlefield being moved into, they cannot play Sprite Call there.

Nuances:

• Moving units is not an "action" in the card sense (actions are cards that say "Action" on them)
• When defending a battlefield you control, you can play sprites to that battlefield during the showdown
• Other cards like Zenith Blade that introduce units through different mechanics may allow units to enter contested battlefields under specific circumstances