Complex sentence: Horner's career in motorsport started after winning a Formula Renault scholarship in 1991, he competed in the 1992 British Formula Renault Championship with Manor Motorsport, finishing that season as a race winner and the highest placed rookie.
Split into simpler sentences: Horner's career in motorsport started after winning a Formula Renault scholarship in 1991. He competed in the 1992 British Formula Renault Championship with Manor Motorsport, finishing that season as a race winner and the highest placed rookie.