Can I still work with other brands on the side?

Yes, with one nuance: if a brand asks for a non-compete, it's stated explicitly in that collab's briefing. No hidden clauses. For other brands in other categories you stay completely free.

Beyond that, we of course expect you to act ethically: don't embrace a direct competitor right after a Wowow collab. Sportfluencer work is a long-term thing, not a sprint.