Complex sentence: They were probably the most feared firm in the 70's and 80's as their pimary purpose was to cause trouble and fights at Millwall football matches, and on occasion, were blamed for causing some of the worst acts of rioting in British football.
Split into simpler sentences: They were probably the most feared firm in the 1970's and 1980's as their pimary purpose was to cause trouble and fights at Millwall FC football matches. On occasion they were blamed for causing some of the worst acts of rioting in British football.