Why did the Kai'Sa player channel 3 runes on their first turn and the Master Yi player channel 4 runes on their first turn?

Ruling: There is a battlefield card that causes players to channel an extra rune on their first turn of the game.

Sequence:

• First player (Kai'Sa) channels 3 runes (2 base + 1 from battlefield)
• Second player (Master Yi) channels 4 runes (3 base + 1 from battlefield)

Nuances:

• This is a battlefield-specific effect, not a core rule
• The second player normally channels one more rune than the first player, and the battlefield bonus applies to both players