Arjuna saves Bhishma from Krishna
You can read more about Bhishma at Wikipedia: "there was an intense battle between Bhishma and Arjuna. Although Arjuna was very powerful, he was no match for Bhishma. Bhishma soon shot arrows which cut Arjuna's armour and then also his Gandiva bow's string. Arjuna was helpless before the wrath of his grand-uncle. As Bhishma was about to kill Arjuna with his arrows, Sri Krishna who took vow of not raising a weapon in the war, lifted a chariot wheel and threatened Bhishma. Arjuna stopped Lord Krishna. Arjuna convinced Krishna to return to the chariot and put down the wheel, promising to redouble his determination in the fight. Thus Bhishma fulfilled his vow."