SEASON 3
(Thanks to John for this summary!)

TO FIGHT OR NOT TO FIGHT 
(Episode 3)

After a sneak attack from Renamon, Guilmon tried to fight.  His eyes became cold and he wasn't like the Guilmon that was seen before. 

Luckily before it got out of hand Terriermon came and stopped the fight.  Later that evening Guilmon ran off with the same cold eyes as before. 

Takato ran after them and they ended up in a parking garage where Renamon and Rika were waiting.