His career as a professional started on 31 October 1786 at Long Fields, when he fought John Boone, who was known as "The Fighting Grenadier". Toughs broke into the ring and ganged up on Brain. In the resulting melée, Brain suffered a beating that almost closed one of his eyes. When order was restored and a surgeon had lanced the swelling around the eye, he resumed fighting and within thirty minutes had forced Boone to quit in defeat.
