SB 10.74.43

tāvad utthāya bhagavān
 svān nivārya svayaṁ ruṣā
śiraḥ kṣurānta-cakreṇa
 jahāra patato ripoḥ
Synonyms: 
tāvat — at that point; utthāya — rising; bhagavān — the Supreme Lord; svān — His own (devotees); nivārya — stopping; svayam — Himself; ruṣā — angrily; śiraḥ — the head; kṣura — sharp; anta — whose edge; cakreṇa — with His disc weapon; jahāra — severed; patataḥ — attacking; ripoḥ — of His enemy.
Translation: 
At that point the Supreme Lord stood up and checked His devotees. He then angrily sent forth His razor-sharp disc and severed the head of His enemy as he was attacking.
Purport: 

Śrīla Viśvanātha Cakravartī Ṭhākura explains the Lord’s action as follows: If Lord Kṛṣṇa had done nothing, there probably would have been a savage fight on the sacrificial grounds, and thus the whole ceremony would have been drenched in blood, spoiling the sanctified atmosphere. Therefore, in order to protect the Rājasūya sacrifice of Kṛṣṇa’s beloved devotee Yudhiṣṭhira, the Lord immediately severed Śiśupāla’s head with His razor-sharp disc in such a way that not a drop of blood fell within the sacrificial grounds.