However, attendances fell at the turn of the 1980s as Derby were relegated from the First Division in 1980, and in 1984 they fell into the Third Division, though an upswing in form followed and they were back in the First Division by 1987. Perimeter fencing was erected between the stands and the pitch during the 1970s to combat pitch invasions by hooligans, but this was dismantled in April 1989, within days of the Hillsborough disaster in which 96 Liverpool fans were fatally injured, most of them crushed to death against perimeter fencing. This resulted in policing levels in games at the Baseball Ground being increased by 50%.