SB 10.78.28
etavad uktva bhagavan
nivrtto ’sad-vadhad api
bhavitvat tam kusagrena
kara-sthenahanat prabhuh
Translation:
[Sukadeva Gosvami continued:] Although Lord Balarama had stopped killing the impious, Romaharsana’s death was inevitable. Thus, having spoken, the Lord killed him by picking up a blade of kusa grass and touching him with its tip.
Purport:
Srila Prabhupada writes: “Lord Balarama had avoided taking part in the Battle of Kuruksetra, and yet because of His position as an incarnation, the reestablishment of religious principles was His prime duty. Considering these points, He killed Romaharsana Suta simply by striking him with a kusa straw, which was nothing but a blade of grass. If someone questions how Lord Balarama could kill Romaharsana Suta simply by striking him with a blade of kusa grass, the answer is given in the Srimad-Bhagavatam by the use of the word prabhu, ‘master.’ The Lord’s position is always transcendental, and because He is omnipotent He can act as He likes without being obliged to follow the material laws and principles. Thus it was possible for Him to kill Romaharsana Suta simply by striking him with a blade of kusa grass.”