A healthy 23-year-old man suffered a helmet-to-helmet collision with an opponent during a game of American football. He immediately experienced transient blurred vision for a few minutes and mild nausea and dizziness, without amnesia. The symptoms improved within 15 min and the team director allowed him to return to play the next day. Three days later, he was again hit on the head while playing American football. He subsequently experienced continuous vomiting and dizziness. He visited our hospital 18 h after sustaining the second injury. On admission, he showed mild dizziness without cerebellar sign. Magnetic resonance imaging (MRI) revealed acute infarction in the right cerebellar hemisphere (Fig. 1A-D), and magnetic resonance angiography (MRA) revealed stenosis of the right superior cerebellar artery (SCA) without vertebral artery (VA) dissection (Fig. 2A). Although vasculitis, autoimmune diseases, encephalitis, and cardiogenic cerebral embolism were considered, laboratory and cardiac investigations yielded normal results. We therefore diagnosed cerebellar infarction due to traumatic arterial spasm or dissection of the SCA and started conservative treatment. Dizziness gradually improved, and MRA 3 days after the second injury revealed improved stenosis of the right SCA (Fig. 2B). Vertebral angiography 7 days after the second injury demonstrated no abnormalities (Fig. 3A-C). The patient was discharged home, after 2 weeks, without neurological deficits. Follow-up MRI and MRA 3 months after the second injury revealed old infarction in the right cerebellar hemisphere without vascular abnormality (Fig. 2C).