Complex sentence: Everton was a talented amateur billiards player, reaching both the 1975 and 1977 world semi-finals, where in the latter he exacerbated a back injury forcing an early retirement from the highest level of the game.
Split into simpler sentences: Everton was a talented amateur billiards player, reaching both the 1975 and 1977 world semi-finals. In the latter he exacerbated a back injury, forcing his early retirement from the highest level of the game.