SB 10.15.36

tataḥ kṛṣṇaṁ ca rāmaṁ ca
 jñātayo dhenukasya ye
kroṣṭāro ’bhyadravan sarve
 saṁrabdhā hata-bāndhavāḥ
tataḥ — then; kṛṣṇam — at Lord Kṛṣṇa; ca — and; rāmam — Lord Rāma; ca — and; jñātayaḥ — the intimate companions; dhenukasya — of Dhenuka; ye — who; kroṣṭāraḥ — the asses; abhyadravan — attacked; sarve — all; saṁrabdhāḥ — enraged; hata-bāndhavāḥ — their friend having been killed.
The other ass demons, close friends of Dhenukāsura, were enraged upon seeing his death, and thus they all immediately ran to attack Kṛṣṇa and Balarāma.

Śrīla Sanātana Gosvāmī makes the following comment on this verse: “It is stated here that the ass demons first attacked Kṛṣṇa and then Balarāma (kṛṣṇaṁ ca rāmaṁ ca). One reason for this is that the demons, having seen the prowess of Lord Balarāma, thought it wise to attack Kṛṣṇa first. Or it may be that out of affection for His elder brother, Lord Kṛṣṇa placed Himself between Balarāma and the ass demons. The words kṛṣṇaṁ ca rāmaṁ ca may also be understood to indicate that Lord Balarāma, out of affection for His younger brother, went to Lord Kṛṣṇa’s side.