etāvad uktvā bhagavān
nivṛtto 'sad-vadhād api
bhāvitvāt taḿ kuśāgreṇa
kara-sthenāhanat prabhuḥ
etavat -- this much; uktva -- saying; bhagavan -- the Personality of Godhead; nivrittah -- stopped; asat -- the impious; vadhat -- from killing; api -- although; bhavitvat -- because it was inevitable; tam -- him, Romaharshana; kusa -- of kusa grass; agrena -- with the tip of a blade; kara -- in His hand; sthena -- held; ahanat -- killed; prabhuh -- the Lord.
[Sukadeva Gosvami continued:] Although Lord Balarama had stopped killing the impious, Romaharshana'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.
Srila Prabhupada writes, "Lord Balarama had avoided taking part in the Battle of Kurukshetra, and yet because of His position, the reestablishment of religious principles was His prime duty. Considering these points, He killed Romaharshana 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 Romaharshana 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 Romaharshana Suta simply by striking him with a blade of kusa grass.''
