Big Cliff made a habit of winning the Dartsathlon (an event made up of having 15 darts at various doubles, trebles, Bullseyes, 25s, and 501 legs) in the early–mid 80s winning the event four times in 1982, 1983, 1985, and 1986.
The passage describes Big Cliff as a successful darts player who won the Dartsathlon four times between 1982 and 1986. The event involved various scoring opportunities like doubles, trebles, bullseyes, 25s, and 501 legs.