Complex sentence: LittleFoot can go into a'berserker' mode when stressed.That LittleFoot knows how to fend for itself when Bitey was blocking the way back to the Bigfoot.
Split into simpler sentences: LittleFoot can go into a'berserker' mode when stressed. A LittleFoot knew how to fend for itself when Bitey was blocking its way back to the Bigfoot.