Complex sentence: He states that roughly half of the team's hooligans became involved in selling class A drugs, partly because of the wave of drugs that came with early 1990s rave culture, a scene that football hooligans were at the centre of.
Split into simpler sentences: He states that roughly half of the team's hooligans became involved in selling class A drugs. This was partly due to the wave of drugs that came with early 1990s rave culture, a scene that football hooligans were at the centre of.